Raynaud's Phenomenon

Raynaud's phenomenon is episodic vasospasm of the small arteries and arterioles supplying the fingers — and, less often, the toes, ears, nose, and nipples — triggered by cold exposure or emotional stress and producing a characteristic sequence of colour change: white, then blue, then red.^[1] It is genuinely common, with population estimates for primary Raynaud's phenomenon in the range of 3-5% of adults, a strong female predominance, and a materially higher prevalence in colder climates — making this a genuinely Canadian-winter-relevant condition a community pharmacist will see regularly, not an imported curiosity.^[1][2]

The single most important framing point in this chapter is the distinction between primary and secondary Raynaud's phenomenon. Primary Raynaud's phenomenon — sometimes still called Raynaud's disease — is a functional vasospastic disorder with no identifiable underlying cause, typically begins in the teens or twenties, follows a symmetric and comparatively mild pattern, and carries an essentially benign long-term course with no tissue damage.^[3][1] Secondary Raynaud's phenomenon reflects an identifiable underlying disease process — most importantly connective tissue disease, and above all systemic sclerosis (scleroderma), in which Raynaud's phenomenon is the presenting symptom in the great majority of patients and can precede the disease's other manifestations by years — and carries a genuine, non-theoretical risk of digital ulceration, critical digital ischemia, and tissue loss that primary disease essentially never does.^[1][4]

This chapter covers the primary-versus-secondary distinction and the bedside and laboratory features that separate them, the classic tricolour sequence and its triggers, a genuine centrepiece drug-induced and drug-worsened Raynaud's phenomenon table — beta-blockers, ergot alkaloids and triptans, specific chemotherapy agents, clonidine, decongestants, ADHD stimulants, and interferons are all real, common, and frequently overlooked contributors a pharmacist is uniquely well positioned to catch on medication review — non-pharmacologic measures as genuine first-line treatment, dihydropyridine calcium channel blockers as first-line pharmacotherapy, and the escalation ladder (phosphodiesterase-5 inhibitors, topical nitrates, and, for severe or ulcerating secondary disease, intravenous prostanoids and surgical sympathectomy) reserved for disease that does not respond to first-line measures.

The classic tricolour sequence

A textbook Raynaud's attack passes through three phases, each with its own distinct mechanism.^[1]

• White (pallor) — an abrupt, well-demarcated vasospasm of the digital arteries and cutaneous arterioles cuts off blood flow almost completely, producing a sharply demarcated white or waxy digit, often with numbness or a "dead finger" sensation.
• Blue (cyanosis) — as the vasospastic phase continues, the small amount of blood still present in the capillaries and venules desaturates, producing a dusky blue-purple colour, frequently accompanied by aching or throbbing discomfort.
• Red (reperfusion/rubor) — once the vasospasm resolves, a brisk reactive hyperemia floods the digit with blood, producing a bright red colour, often with throbbing pain, tingling, or a burning sensation as sensation and circulation return.

The classic tricolour sequence of a Raynaud's phenomenon attack in a 25-year-old man with systemic lupus erythematosus: pallor from vasospasm, cyanosis as residual blood desaturates, and rubor on reperfusion. (Tcal/Patrick Callahan, CC BY-SA 3.0, Wikimedia Commons)

Not every attack — and not every patient — passes through all three phases in a clean sequence; a biphasic pattern (white-then-blue, or white-then-red) or even a monophasic pallor-only attack is still entirely consistent with Raynaud's phenomenon.^[1][2] Insisting on a textbook-perfect triphasic history before accepting the diagnosis is a common and avoidable error (see Common Errors to Avoid). What is genuinely required for the diagnosis is a well-demarcated colour change of the digit(s) — not simply "cold hands" or diffuse mottling.^[2]

Triggers and distribution

Cold exposure is the classic trigger — and not only obvious cold, but comparatively subtle everyday exposures a patient may not connect to the diagnosis: reaching into a freezer or refrigerated grocery aisle, holding a cold drink, air conditioning, or a drop in ambient temperature well short of what most people would call "cold." Emotional stress is an independent trigger through the same sympathetically mediated vasospastic pathway, and the two commonly compound each other.^[1] Attacks most often affect the fingers, typically sparing the thumb, and are frequently symmetric in primary disease; the toes, ears, nose, and nipples can also be affected, and Raynaud's phenomenon of the nipple is a real, under-recognized cause of pain during breastfeeding (see Special Populations).^[1]

Primary versus secondary Raynaud's phenomenon — the central diagnostic distinction

Diagnostic classification criteria

Two complementary, widely used frameworks anchor the primary-versus-secondary distinction in practice. The original LeRoy and Medsger criteria define primary Raynaud's phenomenon by the presence of symmetric attacks, no evidence of peripheral vascular disease, no digital pitting/ulceration/gangrene, a normal nailfold capillaroscopy, a negative ANA, and a normal erythrocyte sedimentation rate — correctly classifying roughly 89% of patients at initial evaluation in the original validation cohort.^[3] A subsequent international Delphi consensus (Maverakis et al.) refined the core diagnostic criteria to two required elements — patient-reported cold- or emotional-stress-triggered acral colour change, together with a biphasic colour response (pallor and/or cyanosis, plus erythema during recovery) — while retaining the same underlying primary-versus-secondary framework for the subsequent workup.^[2]

Secondary causes beyond connective tissue disease

Not every case of secondary Raynaud's phenomenon is autoimmune. Consider and screen for: occupational vibration exposure (hand-arm vibration syndrome, from power tools — a real, compensable occupational condition worth asking about directly); thoracic outlet syndrome or another proximal arterial compression/embolic source, particularly with strictly unilateral symptoms; atherosclerotic peripheral arterial disease in an older patient with vascular risk factors; thromboangiitis obliterans (Buerger disease) in a younger patient who smokes; hypothyroidism; paraproteinemia or cryoglobulinemia; and drug-induced or drug-worsened Raynaud's phenomenon — a genuinely common and frequently overlooked cause covered as this chapter's centrepiece (see Drug Tables and Choose Initial Treatment).^[1][5]

Differential diagnosis at a glance

• Female sex — primary Raynaud's phenomenon is roughly 3-4 times more common in women.^[1]
• Family history of Raynaud's phenomenon.
• Younger age (primary disease) — typical onset in the teens to twenties.^[3]
• Residence in, or regular exposure to, a cold climate — genuinely relevant to Canadian practice.^[1]
• Tobacco use — nicotine is directly vasoconstrictive and both triggers and worsens attacks.
• Migraine history — both conditions share an underlying vasospastic tendency.
• Any connective tissue disease, especially systemic sclerosis, systemic lupus erythematosus, Sjögren syndrome, dermatomyositis/polymyositis, mixed connective tissue disease, or rheumatoid arthritis.^[4]
• Occupational exposure to vibrating tools (hand-arm vibration syndrome).
• Hypothyroidism.
• Atherosclerotic vascular disease and its usual risk factors, in an older patient presenting with new symptoms.
• Any medication from the drug-culprit table — beta-blockers, ergot alkaloids/triptans, specific chemotherapy agents, clonidine, decongestants, ADHD stimulants, and interferons chief among them (see Drug Tables).^[5]
• Repeated local cold injury, including a prior frostbite injury to the same digit.

History

Characterize the attack itself: distribution (symmetric versus asymmetric or single-digit), age of first attack, frequency, duration, and whether the classic colour sequence — or a biphasic/monophasic variant — is present.^[2] Ask specifically about digital ulceration, pitting, or any wound that has not healed normally. Screen for connective-tissue-disease features: joint pain or swelling, skin tightening or thickening, dysphagia or new reflux, dry eyes or mouth, proximal muscle weakness, and unexplained weight loss. Take a complete medication history, including over-the-counter products (decongestants) and any recent dose change, and correlate the timeline of any new symptom against the medication list rather than treating this as a separate, later step — this is exactly where a pharmacist's structured medication review adds real diagnostic value.^[5] Ask about occupational vibration exposure, smoking, and family history of Raynaud's phenomenon or connective tissue disease.

Examination

Examine the digits for pitting scars, active ulceration, sclerodactyly, digital swelling ("puffy fingers"), calcinosis, and telangiectasia. Check peripheral pulses and consider an Allen test if a proximal arterial or embolic cause is suspected. A single-digit or strictly unilateral presentation should prompt a more focused vascular examination, including for signs of thoracic outlet syndrome.

Nailfold capillaroscopy

A simple, non-invasive, in-office technique — a drop of oil is placed at the nailfold and the capillary bed is examined under magnification (a dermatoscope is often sufficient; a dedicated capillaroscope offers more detail) — that is genuinely useful for separating primary from secondary disease. Normal, regularly spaced capillary loops support primary disease; the "scleroderma pattern" — capillary dropout (avascular areas), enlarged or giant capillaries, and microhemorrhages — strongly suggests secondary disease, particularly systemic sclerosis, and should prompt rheumatology referral even before autoantibody results return.^[7][2]

Laboratory investigations

For any patient with a red flag (see Red Flags & Refer): ANA, with reflex to an extended autoantibody panel (anti-centromere, anti-topoisomerase I/anti-Scl-70, anti-RNA polymerase III, and other connective-tissue-disease-associated antibodies as clinically indicated) if positive; complete blood count and inflammatory markers (ESR/CRP); and thyroid-stimulating hormone. Consider serum protein electrophoresis and cryoglobulins if paraproteinemia or a cryoglobulinemic process is suspected. A patient with a normal examination, normal nailfold capillaries, and no red flags does not require this full panel — over-investigating straightforward primary disease is its own avoidable error.

Applying the classification criteria

Apply the LeRoy-Medsger and international consensus criteria (see Recognize the Condition) systematically rather than relying on gestalt — a patient meeting every primary-disease criterion (symmetric attacks, no ulceration, normal capillaries, negative ANA, normal ESR) can be reassured and managed as primary disease; any single secondary-disease feature should prompt the fuller workup above and, where confirmed or strongly suspected, rheumatology referral.^[3][2]

Differential diagnosis

See Recognize the Condition for the full comparison table (acrocyanosis, erythromelalgia, chilblains, frostbite, peripheral arterial disease, carpal tunnel syndrome, and complex regional pain syndrome as the principal alternatives to actively distinguish).

• Correctly classify primary versus secondary Raynaud's phenomenon before committing to a treatment intensity, since the two carry genuinely different urgency and risk.
• Reduce attack frequency, severity, and duration to a level the patient finds tolerable and that preserves function.
• Prevent digital ulceration and critical ischemia in secondary disease — this is the goal that actually matters clinically, not simply "fewer colour changes."
• Identify and address every modifiable drug-induced or drug-worsening contributor through a structured medication review, in collaboration with the prescriber.
• Support smoking cessation specifically because of its direct vasoconstrictive relevance, not as generic health advice.
• Exhaust non-pharmacologic measures before, and alongside, any pharmacotherapy for mild-to-moderate primary disease.
• Use the lowest effective calcium channel blocker dose, titrating to symptom control and tolerability rather than a fixed target dose.
• Escalate promptly — not after a prolonged trial-and-error period — once digital ulceration or critical ischemia is present.
• Refer secondary disease, and any red flag, for rheumatologic and/or vascular assessment rather than managing it indefinitely in isolation.

Step 1 — Non-pharmacologic measures, for every patient

Preferred approach implement the full set of measures in Non-Pharmacologic Treatment — whole-body and local warming, layered clothing, smoking cessation, and trigger avoidance — as first-line management for every patient, including one ultimately started on a calcium channel blocker. For mild, infrequent primary disease, non-pharmacologic measures alone are often genuinely sufficient and no drug is needed.^[1]

Step 2 — Structured medication review

Preferred approach systematically check every medication against the drug-culprit table (see Drug Tables). Situational where a flagged drug is genuinely needed for its primary indication (a beta-blocker after myocardial infarction, an ADHD stimulant with a clear functional benefit), discuss a dose reduction, a within-class substitution to a lower-risk agent, or — only in collaboration with the prescriber — a taper and discontinuation, rather than a pharmacist or patient stopping it unilaterally.^[5]

Step 3 — Calcium channel blocker, when symptoms remain significant

1st-line pharmacotherapy a dihydropyridine calcium channel blocker — oral nifedipine, extended-release, is the best-studied agent — should be used first-line once non-pharmacologic measures and medication optimization leave symptoms frequent, severe, or functionally limiting, and is appropriate first-line pharmacotherapy for secondary as well as primary disease.^[8] Start at a low dose and titrate upward against symptom control and tolerability (hypotension, headache, peripheral edema, reflex tachycardia); use the extended-release formulation rather than a short-acting one, which carries a materially higher risk of reflex tachycardia and hypotension without a corresponding efficacy benefit (see Common Errors to Avoid). Alternative felodipine or amlodipine (the latter available in this catalogue only as a fixed-dose combination product) are reasonable alternative dihydropyridines if nifedipine is not tolerated.^[8]

Step 4 — Escalation for inadequate response or secondary disease

Escalate once a calcium channel blocker at the maximum tolerated dose does not adequately control symptoms — or immediately, in parallel with the calcium channel blocker, for secondary disease with digital ulceration or a high-risk connective-tissue-disease pattern — add a phosphodiesterase-5 (PDE5) inhibitor (sildenafil or tadalafil) and/or a topical nitrate; losartan or fluoxetine are reasonable alternative or adjunct agents with their own supporting trial evidence.^[8][9]

Step 5 — Severe, refractory, or ulcerating secondary disease

Specialist-directed for digital ulceration or critical digital ischemia that does not respond to maximized combination oral therapy, intravenous prostanoid therapy (iloprost) is the guideline-endorsed escalation, administered at a specialized centre; botulinum toxin injection into the digital neurovascular bundles is a reasonable adjunct or alternative in refractory cases; and surgical digital sympathectomy is reserved for critical ischemia refractory to maximal medical therapy.^[8] This tier of care needs rheumatology and/or vascular surgery co-management — see Red Flags & Refer and the Clinical Decision Algorithm.

Warming — whole-body, not just local

Layered clothing and mittens (rather than gloves — keeping the fingers together conserves heat more effectively than separating them) are the mainstay, but the single most under-taught point is that core body warmth matters as much as local hand warmth: a cold torso itself triggers reflex peripheral vasoconstriction, so a well-insulated hat, scarf, and coat genuinely help protect the fingers, not only warm mittens on their own.^[1] Chemical or battery hand and foot warmers are a simple, effective adjunct for outdoor exposure. At the first sign of an attack, warm water immersion of the affected digit(s) — not hot water, which risks a thermal injury to a digit with reduced sensation during the attack — will usually abort it.

Avoiding predictable triggers

• Abrupt cold exposure with no warning — reaching into a freezer or refrigerated grocery case, air conditioning set aggressively cold, or handling a cold drink — is a genuinely common and underappreciated trigger; anticipate and protect against it, not only obvious outdoor cold.
• Emotional stress — where feasible, stress-reduction techniques and biofeedback have modest supporting evidence and are a reasonable adjunct for a motivated patient.
• Occupational vibrating tools — workplace modification (anti-vibration gloves, tool substitution, scheduled breaks) where hand-arm vibration syndrome is a contributing factor.
• Caffeine — evidence is weaker and mixed, but a trial of reduced intake is reasonable and low-risk for a patient motivated to try it.

Smoking cessation

Directly relevant, not generic advice nicotine is directly vasoconstrictive and both triggers and worsens Raynaud's attacks^[1] — frame cessation counselling around this specific, immediate mechanism rather than only long-term cardiovascular risk, since a patient may respond better to "this is actively causing your finger attacks" than to generic anti-smoking messaging. Offer pharmacotherapy and connect the patient with cessation supports rather than a simple instruction to stop.

Trigger-drug avoidance, where feasible

Cross-reference the drug-culprit table (see Drug Tables) at every visit — avoiding a genuinely avoidable vasoconstrictive medication (an OTC decongestant during cold-and-flu season, for example) is a simple, high-value, and often overlooked non-pharmacologic intervention.^[5] For a prescription medication, this needs prescriber collaboration rather than unilateral patient action (see Choose Initial Treatment).

General measures

• Regular aerobic exercise supports overall vascular health and is not contraindicated by Raynaud's phenomenon itself, though outdoor exercise in cold weather needs the same layering and warming precautions.
• Maintain adequate hydration.
• Protect the digits from even minor trauma in secondary disease, where a small cut or hangnail can become a genuine, slow-healing ulcer rather than a trivial injury.
• A symptom diary (frequency, duration, severity, and any identified trigger) is genuinely useful both for the patient's own trigger-avoidance and for objectively judging treatment response at follow-up.

Pregnancy and breastfeeding — including Raynaud's phenomenon of the nipple

Raynaud's phenomenon of the nipple is a real, genuinely under-recognized cause of significant nipple pain during breastfeeding, distinct from the far more commonly assumed causes (poor latch, candidal infection, or bacterial mastitis). It presents as episodic nipple blanching — classically triggered by the cold immediately after a feed as the nipple is exposed to air, or by the mechanical stimulus of latch itself — followed by cyanosis and/or a painful red, throbbing reperfusion phase, and is easily misattributed to thrush if this specific trigger pattern is not asked about directly.^[1] Confirm latch technique first, keep the nipple warm and dry immediately after feeds, and avoid caffeine and nicotine; if pharmacotherapy is genuinely needed, oral nifedipine (extended-release) is the best-studied option and is considered compatible with breastfeeding.^[8] For pregnancy generally, dihydropyridine calcium channel blockers, with nifedipine again the best-established, are considered a reasonable choice when pharmacotherapy is needed; avoid losartan, which is contraindicated in pregnancy, and reassess any drug-culprit medication in the context of pregnancy-specific safety, not only Raynaud's-specific risk.

Pediatrics

Most children presenting with Raynaud's phenomenon have primary disease with a genuinely benign course, but a positive ANA, a connective-tissue-disease-associated autoantibody, or abnormal nailfold capillary changes should prompt referral to pediatric rheumatology and closer follow-up, since these findings identify a real subset at risk for an evolving systemic disease.^[6] Reassurance and non-pharmacologic measures are the mainstay for straightforward pediatric primary disease; pharmacotherapy trial evidence in children is limited, and a calcium channel blocker trial, when genuinely needed, should be undertaken with the same low-dose, gradually titrated approach as in adults.^[6]

Older adults

New Raynaud's phenomenon presenting for the first time in an older adult is more likely to be secondary — screen actively for atherosclerotic peripheral arterial disease and for a drug-induced cause, which is disproportionately likely in this group given typical polypharmacy (a beta-blocker for a cardiac indication is a common, easily overlooked culprit).^[5] Calcium channel blockers are generally well tolerated but watch more closely for hypotension and peripheral edema.

Systemic sclerosis (scleroderma) and other connective tissue disease

This is the population carrying the great majority of the genuine digital-ulceration and critical-ischemia risk this chapter is centred on preventing, and the population the escalation ladder in Choose Initial Treatment and the Clinical Decision Algorithm is largely built around.^[8][4] Close co-management with rheumatology (and vascular surgery once ulceration or critical ischemia develops) is appropriate rather than managing this group purely in primary care or community pharmacy. Digital ulcer wound care, prompt recognition of superimposed infection, and avoiding premature or overly pessimistic conversations about amputation before a wound has had adequate time and specialist assessment are all genuinely relevant here, echoing the same demarcation-before-amputation principle covered in more depth in this platform's separate Frostbite chapter.

Occupational hand-arm vibration syndrome

Where vibrating-tool exposure is a contributing factor, workplace modification (anti-vibration equipment, tool substitution, scheduled breaks, and glove use) is a genuine and often underused intervention; consider whether an occupational health or workers' compensation referral is appropriate.

Renal and hepatic impairment

Dihydropyridine calcium channel blockers require little renal dose adjustment but should be used cautiously in significant hepatic impairment, where clearance is reduced. Sildenafil and tadalafil both require dose adjustment in significant renal or hepatic impairment — confirm the current recommendation against each drug's own Drug Database entry before use. Losartan requires caution in significant renal impairment given its effect on potassium and renal hemodynamics.

Reassess attack frequency, severity, and duration at every follow-up, ideally against the patient's own symptom diary rather than relying on recall alone — this is what actually judges whether a change (non-pharmacologic, medication adjustment, or a new drug) is working.^[1]

• Examine the digits specifically for new pitting, ulceration, or any sign of tissue breakdown at every visit in a patient with known or suspected secondary disease — this is the single highest-yield follow-up action in this chapter for the population that actually loses tissue.
• Check blood pressure and heart rate, and ask about peripheral edema, at each calcium channel blocker dose titration.
• Reassess the primary-versus-secondary classification over time, not only at the initial visit — secondary features (new ulceration, new autoantibody positivity, evolving skin changes) can emerge later in a patient initially and correctly classified as primary at first presentation.^[3]
• Reconcile the full medication list at every visit for a newly started or dose-increased culprit drug, not only at the original diagnosis.^[5]
• Reassess smoking status and reinforce cessation support at every visit where relevant.
• For a patient on combination pharmacotherapy (calcium channel blocker plus a PDE5 inhibitor and/or topical nitrate), confirm the added agent is genuinely contributing before continuing it indefinitely — deprescribe an agent that has not produced a meaningful benefit after an adequate trial.
• For secondary disease under specialist co-management, confirm the patient is actually attending rheumatology/vascular follow-up rather than assuming this is happening.

1. Confirm non-pharmacologic measures were actually implemented correctly — whole-body warming technique, trigger avoidance, and smoking cessation are frequently under-taught or only partially adopted rather than genuinely ineffective; re-teach and reassess before escalating.
2. Confirm the calcium channel blocker was titrated to the maximum tolerated dose, using the extended-release formulation, before concluding it has failed — an inadequate dose or a short-acting formulation is a common, correctable reason for apparent treatment failure.
3. Re-screen the full medication list for a second, less obvious culprit drug — a patient on more than one relevant agent (for example, a decongestant taken during a cold on top of a baseline beta-blocker) commonly has more than one contributor, and addressing only the first one found is a common source of apparent treatment failure.
4. Reassess the primary-versus-secondary classification if it has not been revisited recently — new digital ulceration, new autoantibody positivity, or evolving skin changes can emerge after an initial primary-disease classification and change the entire management plan.
5. Add a phosphodiesterase-5 inhibitor and/or a topical nitrate if not already tried; consider losartan or fluoxetine as an alternative or additional adjunct.
6. For digital ulceration or critical digital ischemia not responding to maximized combination oral therapy: refer urgently for intravenous iloprost at a specialized centre; consider botulinum toxin injection as an adjunct or alternative under specialist care.
7. For critical ischemia refractory to maximal medical therapy: surgical digital sympathectomy is a genuine, if last-resort, option — this decision belongs with vascular surgery, not primary care or community pharmacy.
8. Throughout escalation, confirm no new red flag has appeared that changes the referral urgency (see Red Flags & Refer) — treatment failure in a patient with new ulceration is not simply "try the next drug," it is a trigger for urgent specialist involvement.

• Assuming every case of Raynaud's phenomenon is benign primary disease without actively screening for the secondary-disease red flags.
• Insisting on a textbook-perfect white-blue-red triphasic history before accepting the diagnosis — a biphasic or monophasic colour change is still genuine Raynaud's phenomenon.
• Missing a "hidden" culprit drug — ophthalmic timolol, an OTC decongestant, or an ADHD stimulant are all real, common, and easy to overlook if the medication review is limited to obvious oral cardiovascular drugs.
• Stopping a needed beta-blocker (for example, one started after myocardial infarction) unilaterally rather than discussing dose reduction, substitution, or a supervised taper with the prescriber.
• Prescribing or recommending short-acting immediate-release nifedipine instead of an extended-release formulation, risking reflex tachycardia and hypotension without added efficacy.
• Advising only local hand warming while overlooking the genuine contribution of whole-body/core cold exposure to triggering an attack.
• Confusing Raynaud's phenomenon with erythromelalgia — the two are pathophysiologic opposites (vasospasm versus vasodilation), and a vasodilating treatment appropriate for one can worsen the other.
• Delaying rheumatology referral in a patient with new digital ulceration or pitting while continuing to manage it as routine primary-disease follow-up.
• Attributing nipple pain during breastfeeding to thrush or poor latch without asking about the specific cold-triggered blanching pattern of Raynaud's phenomenon of the nipple.
• Starting losartan in a woman of childbearing age without confirming pregnancy status or plans first.
• Treating "cold hands" or diffuse mottling without a well-demarcated colour change as Raynaud's phenomenon.
• Not reassessing the primary-versus-secondary classification over time, assuming an initial benign classification holds indefinitely.

How to use this table: Doses are adult doses and require patient-specific confirmation (renal/hepatic function, weight, allergy history). Pediatric dosing is weight-based per the current product monograph unless stated. Drug pricing is intentionally omitted. Select any drug name to open its complete Pharmasist Drug Database page.

Beta-Blockers

The single most common secondary-Raynaud's-associated drug class — non-selective agents carry the strongest association, but cardioselective agents and even ophthalmic (eye-drop) formulations are genuinely capable of causing or worsening attacks through systemic absorption.^[5]

Ergot Alkaloids and Triptans

Both classes act on serotonergic and/or alpha-adrenergic receptors to produce direct vasoconstriction — genuinely useful for aborting a migraine, but the same mechanism can precipitate or worsen Raynaud's phenomenon.

Chemotherapy Agents

Well documented specifically with combination regimens for germ-cell (testicular) cancer — bleomycin and cisplatin carry the strongest individual association, and the combination of bleomycin with vinblastine carries a materially higher risk than bleomycin with etoposide. Onset is typically 3-6 months after starting therapy and can persist for years after treatment ends.^[10]

Clonidine and Other Centrally Acting Alpha-2 Agonists

A well-recognized, if under-appreciated, cause — the same alpha-2-agonist mechanism that lowers blood pressure centrally also enhances cold-amplified peripheral alpha-2c-receptor-mediated vasoconstriction.

Decongestants and Other Sympathomimetics

Direct alpha-adrenergic agonists — genuinely common, easy-to-overlook culprits precisely because they are over-the-counter and often taken only intermittently for a cold or allergy symptoms rather than as a scheduled medication.

ADHD Stimulants

Both methylphenidate- and amphetamine-class stimulants are recognized causes of new or worsened Raynaud's phenomenon, working through peripheral catecholamine release and reuptake inhibition; amphetamine-class agents (which both release and inhibit reuptake of catecholamines) appear to carry a higher reported risk than methylphenidate-class agents (reuptake inhibition alone).^[11]

Interferons

Recognized specifically with interferon-alfa (oncology, chronic viral hepatitis) and interferon-beta (multiple sclerosis) therapy, with case reports ranging from mild vasospasm to digital ischemia and, rarely, tissue loss; onset can be weeks to years after starting therapy.