Endometriosis

Endometriosis is a chronic, estrogen-dependent inflammatory condition defined by the presence of endometrium-like tissue outside the uterine cavity — most often on the ovaries and the cul-de-sac (rectouterine pouch), though deeper disease can infiltrate the bowel, bladder, ureter, or rectovaginal septum.^[1] It is a heterogeneous disease: the extent of disease found at surgery does not reliably predict pain severity or the chance of pregnancy, and pain and infertility can occur together, separately, or not at all in a given patient.^[2] A major shift in contemporary practice — reflected in current Canadian and European guidance — is that a laparoscopic or histologic diagnosis is no longer required before starting treatment: clinical suspicion supported by history, examination, and (where available) a targeted transvaginal ultrasound is now sufficient grounds to start empiric medical therapy.^[3] This chapter covers pharmacologic management of endometriosis-associated pain and the distinct approach required when infertility, rather than or in addition to pain, is the presenting concern.

Typical presentation

Cyclic pelvic pain that, as disease progresses, can become increasingly acyclic is the dominant symptom — dysmenorrhea, deep dyspareunia, dyschezia (painful defecation, especially perimenstrual), dysuria, and chronic pelvic pain extending beyond the menstrual window. Infertility is the other major presentation, sometimes with no pain at all. On examination, findings suggestive of endometriosis include a fixed, retroverted uterus, adnexal masses, and nodularity or tenderness in the posterior vaginal fornix/cul-de-sac — a normal examination does not exclude the diagnosis.

• Early age of menarche.
• Short menstrual cycle length and prolonged or heavy menstrual flow.
• Family history of endometriosis in a first-degree relative.
• Müllerian tract anomalies causing outflow-tract obstruction.
• Nulliparity.
• Factors associated with lower risk include parity, current hormonal contraceptive use, regular exercise, and omega-3 fatty acid intake — the overall evidence linking lifestyle/dietary factors to endometriosis risk remains limited.

Differentiating endometriosis-associated pelvic pain from its common mimics

These conditions frequently overlap rather than presenting as a clean either/or — a patient with confirmed endometriosis can also have an overlapping chronic pain syndrome, and treating only the endometriosis will leave residual symptoms in that case.

History

• Characterize pain: timing relative to the cycle, dysmenorrhea, deep dyspareunia, dyschezia, dysuria, and chronic (noncyclic) pelvic pain.
• Ask directly about a history of infertility or difficulty conceiving.
• Diagnosis is often significantly delayed — nonspecific symptom presentation, normalization or dismissal of symptoms, and limited access to expert-level pelvic imaging all contribute; keep a low threshold to consider the diagnosis in anyone with pain not explained by primary dysmenorrhea.^[4]

Examination

Look specifically for a fixed, retroverted uterus, adnexal masses, and nodularity or tenderness in the posterior vaginal fornix/cul-de-sac.

Investigations

• Pelvic transvaginal ultrasound is the first-line investigation. A targeted, endometriosis-specific ultrasound protocol can identify both endometriomas and deep infiltrating disease; a standard, non-targeted pelvic ultrasound reliably identifies endometriomas but is much less sensitive for deep disease. Findings are highly operator-dependent.
• MRI is useful for characterizing deep infiltrating lesions, particularly when expert-level endometriosis ultrasound is not accessible.
• Peritoneal (superficial) endometriosis cannot currently be identified on imaging — if peritoneal disease is the specific remaining question after imaging, diagnostic laparoscopy ± biopsy may be considered, though this is no longer a prerequisite for starting treatment.^[2]
• No blood test reliably diagnoses endometriosis. Serum CA-125 is often elevated but is neither sensitive nor specific — it is also elevated in pelvic inflammatory disease, epithelial ovarian cancer, and pregnancy — and should not be ordered as part of routine diagnostic workup.

• Relieve pelvic pain, dysmenorrhea, and dyspareunia.
• Suppress disease activity to reduce the risk of symptom progression and recurrence.
• Preserve or restore fertility potential in patients who desire pregnancy — this requires a fundamentally different approach than pain management.
• Minimize treatment-related adverse effects, particularly the bone mineral density loss associated with prolonged hypoestrogenic therapy.
• Avoid unnecessary surgery while still identifying patients who genuinely need it.
• Address the overlapping chronic pain syndromes that commonly accompany endometriosis, not just the disease itself.

• Pelvic floor physiotherapy — particularly valuable when pelvic floor muscle dysfunction contributes to dyspareunia, dyschezia, or urinary symptoms, and as part of an interdisciplinary chronic pain approach.
• Regular exercise is associated with lower endometriosis risk and is a reasonable general adjunct, though it is not a substitute for disease-directed therapy.
• For any patient on long-term progestin, GnRH agonist, or GnRH antagonist therapy, counsel on bone health: adequate calcium intake (about 1200 mg/day total, preferably through diet) and vitamin D supplementation (400-1000 units/day).
• Refer patients to a dedicated endometriosis patient-support organization (e.g., the Endometriosis Network Canada) for education and community support — the chronic, often years-long nature of this disease benefits from peer and community resources beyond a single clinic visit.
• Provide analgesia and symptom management while a patient awaits surgery or the full effect of a newly started medical therapy, rather than leaving pain untreated in the interim.
• Do not use preoperative hormonal therapy specifically to shrink implants before surgery in the expectation that this will prolong the postoperative pain-free interval, reduce recurrence, or increase pregnancy rates — it does none of these, even though it may reduce implant size.

Breastfeeding

Symptoms frequently remain in remission during breastfeeding provided nursing is frequent and intense enough to suppress ovarian estrogen release; treatment is often not required under these conditions. Prolonged breastfeeding is itself associated with a lower long-term risk of endometriosis. If suppressive therapy is needed while breastfeeding, a progestin-only option is generally preferred over an estrogen-containing one.

Adolescents

Consider endometriosis in an adolescent with dysmenorrhea or pelvic pain that does not respond to NSAIDs and cyclic hormonal therapy. Continuous CHC or a progestin-only option remains first-line. GnRH agonists and antagonists are used more cautiously in this population, given ongoing bone mass accrual through adolescence, and are generally reserved for severe, refractory disease under specialist direction with mandatory add-back therapy.

Patients desiring pregnancy (fertility considerations)

Endometriosis carries a genuine dual burden of pain and infertility, and the two are managed very differently. Ovarian-suppressing hormonal therapy is not used to manage endometriosis-associated infertility — it prevents pregnancy — and is appropriate in this population only if severe pain coexists and fertility is not the immediate goal. For patients actively trying to conceive: conservative surgical excision of minimal-to-mild disease improves spontaneous fecundity; letrozole-based ovulation induction with intrauterine insemination is an option for minimal-to-mild disease with patent tubes; and IVF is generally used when the surgically-assessed Endometriosis Fertility Index is low, other treatments have failed, or male-factor infertility coexists. Fecundity declines and pregnancy-loss risk rises after age 35, supporting a more expedited fertility-focused treatment plan in this group rather than working through the full pain-management ladder first.

Post-hysterectomy and bilateral salpingo-oophorectomy

Menopausal hormone therapy after hysterectomy with bilateral salpingo-oophorectomy for endometriosis should include both estrogen and progestogen, not estrogen alone, even without a uterus — unopposed estrogen can reactivate residual endometriotic tissue. The same combined-therapy principle applies to a patient remaining on an unopposed GnRH agonist.

Renal/hepatic impairment

Danazol is avoided in significant liver disease. Elagolix is contraindicated in severe hepatic impairment. Standard renal precautions apply to NSAID use.

Reassess pain response after an adequate trial of any new therapy — generally at least 3 months — before judging it a failure and switching. For a patient on long-term progestin, GnRH agonist, or GnRH antagonist therapy, consider bone mineral density (DXA) screening, particularly when additional bone-loss risk factors are present, and reinforce calcium/vitamin D counselling at each visit. Monitor for hypoestrogenic symptoms (hot flashes, mood changes, vaginal dryness) with GnRH agonist/antagonist therapy and adjust or add add-back therapy accordingly. Monitor lipids periodically in a patient on danazol. Confirm ongoing contraceptive needs at every visit for a patient not desiring pregnancy — a GnRH agonist or antagonist does not reliably prevent pregnancy on its own and needs a backup method if the patient is sexually active with pregnancy potential. For a patient who underwent surgery, confirm postoperative suppressive therapy has actually been started (unless fertility is being actively pursued) and reassess periodically for symptom recurrence.

1. Confirm adherence and correct use — continuous dosing with no unintended hormone-free interval, correct DMPA injection timing, or a confirmed in-place LNG-IUS/implant — and confirm a genuinely adequate trial (generally more than 3 months) has elapsed before calling a therapy a failure.
2. Reassess for an alternative or coexisting diagnosis — primary dysmenorrhea, adenomyosis, pelvic inflammatory disease, an ovarian cyst, or an overlapping chronic pain syndrome (IBS, bladder pain syndrome, pelvic floor dysfunction) — rather than assuming the same disease has simply progressed.
3. If only one first-line class has been tried (for example, CHC alone), switch to the other first-line class (a progestin option) before escalating further.
4. If both CHC and at least one progestin option have failed an adequate trial, or are contraindicated, escalate to a GnRH agonist with mandatory add-back hormone therapy, or a GnRH antagonist.
5. If pain remains refractory despite adequate hormonal escalation, hormonal therapy cannot be tolerated or is declined, or the patient desires pregnancy, refer for surgical evaluation (diagnostic/therapeutic laparoscopy with excision).
6. After surgery, start or resume suppressive hormonal therapy — unless fertility is being actively pursued — to reduce the risk of symptom and disease recurrence.
7. For pain that persists despite optimized medical and surgical therapy, refer for a multidisciplinary chronic pelvic pain program (pelvic floor physiotherapy, pain specialist, psychological support) — an overlapping chronic pain syndrome is common in this situation and needs its own dedicated treatment approach.

• Requiring a laparoscopic or histologic diagnosis before starting treatment — current Canadian and European guidance supports empiric therapy based on history, exam, and imaging alone.
• Starting a GnRH agonist for anything beyond a brief initial course without mandatory add-back hormone therapy.
• Continuing a GnRH agonist or GnRH antagonist beyond its defined duration limit without a documented bone-health monitoring plan.
• Prescribing any ovarian-suppressing hormonal therapy — CHC, a progestin, or a GnRH agonist/antagonist — to a patient who is actively trying to conceive.
• Assuming a new, unusually severe, or different pain pattern is simply worsening endometriosis without first ruling out ovarian torsion, a ruptured endometrioma, or another acute surgical process.
• Using an NSAID only as-needed rather than on a scheduled basis through the expected pain window, which reduces its effectiveness.
• Overlooking an overlapping chronic pain syndrome (IBS, bladder pain syndrome, pelvic floor dysfunction) in a patient with persistent pain despite adequate disease-directed therapy.
• Not counselling that pain often recurs after stopping any suppressive therapy — including after surgery — and that postoperative hormonal suppression reduces, but does not eliminate, that risk.
• Forgetting that DMPA specifically delays the return of ovulation after discontinuation — important counselling for a patient who may want to conceive in the near future.
• Linking the Drug Database's Levonorgestrel monograph (the oral emergency-contraception formulation) as if it were the levonorgestrel intrauterine system — they are different products with different dosing entirely.

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.

Analgesics

Evidence specifically for NSAID efficacy in endometriosis-associated pain remains limited in quality, though NSAIDs remain a reasonable, low-risk, low-cost first step and are frequently combined with hormonal suppression rather than used alone.^[8]

NSAIDs

First analgesic step. Start at symptom onset and take on a scheduled, not PRN, basis through the expected pain window.

Hormonal Suppression

Combined hormonal contraceptives

Continuous (extended-cycle) use is preferred over cyclic use, given a lower risk of dysmenorrhea recurrence; additional risk from continuous use, beyond the usual CHC risks, has not been demonstrated.

Progestin-only options

Androgen agonist

Gonadotropin-releasing hormone (GnRH) agonists

GnRH agonists initially stimulate, then suppress, pituitary FSH/LH secretion, producing a markedly hypoestrogenic state that induces regression of endometriotic implants.^[3] A temporary symptom flare in the first 1-2 weeks of therapy is common, from the initial FSH/LH stimulation — this can be minimized by starting during the luteal phase or with concurrent aromatase-inhibitor or GnRH-antagonist pretreatment. Symptoms commonly recur within 9-12 months of stopping. Any course extending beyond a brief initial trial requires add-back hormone therapy (below) given the bone mineral density loss associated with prolonged hypoestrogenism.

GnRH agonists

Add-back hormone therapy (mandatory with extended GnRH agonist use)

No single standard regimen exists — any regimen containing an estradiol dose approximately equivalent to 1 mg estradiol-17-beta plus a progestin is considered adequate. Add-back therapy is as effective as GnRH agonist monotherapy for pain relief without meaningfully increasing recurrence risk, and improves — though does not fully abolish — hypoestrogenic adverse effects and bone loss. Avoid in a patient with thromboembolic risk factors.

Gonadotropin-releasing hormone (GnRH) antagonists

Unlike agonists, GnRH antagonists produce dose-dependent hypoestrogenism immediately, without an initial flare, and are as effective as GnRH agonists for pain relief.^[6][7]

GnRH antagonists

Aromatase inhibitors (adjunctive, for refractory pain)

Used together with a CHC, progestin, or GnRH agonist/antagonist — the concurrent hormonal agent blunts the ovarian-cyst formation that aromatase-inhibitor monotherapy would otherwise cause in a premenopausal patient via reflex gonadotropin stimulation. Evidence for this specific combination remains limited to small studies; it is not a standardized first-choice regimen. A separate, well-defined letrozole dosing regimen exists for ovulation induction in endometriosis-associated infertility — see below.

Selective progesterone receptor modulators

Mifepristone has shown benefit for dysmenorrhea and dyspareunia in trials, but it is not available in Canada as a standalone product for this indication — only as a fixed combination with misoprostol for medical termination of pregnancy, an entirely different use. Ulipristal acetate 5 mg (previously marketed for uterine fibroids) was voluntarily withdrawn from the Canadian market due to the risk of serious drug-induced liver injury, including cases requiring liver transplantation.^[9] This withdrawal does not affect the ulipristal acetate 30 mg product used for emergency contraception, which remains available but is not indicated for endometriosis.

Endometriosis-Associated Infertility

Drug therapy directed at endometriosis itself does not improve fecundity, and ovarian-suppressing hormonal therapy is never used to manage infertility since it prevents pregnancy. The agents below are used specifically within a fertility-focused pathway.^[3]

Ovulation induction and assisted conception

A 3-6 month course of a GnRH agonist (see the GnRH agonist table above) before IVF or intracytoplasmic sperm injection — used as pituitary down-regulation, sometimes called superovulation or controlled ovarian hyperstimulation, together with intrauterine insemination for minimal-to-mild disease — improves the odds of clinical pregnancy; live birth rates diminish with successive treatment cycles, and outcomes should be reviewed with a fertility specialist rather than repeated indefinitely.