Relugolix: Oral GnRH Antagonist for Prostate Cancer and Uterine Fibroids
Relugolix is an orally administered gonadotropin-releasing hormone (GnRH) receptor antagonist, representing the first oral agent in this pharmacological class to reach clinical practice. Unlike GnRH agonists, which require an initial period before suppressing testosterone, relugolix produces rapid and competitive blockade of GnRH receptors in the pituitary without triggering the initial hormonal surge associated with agonist administration. This mechanistic distinction has important clinical consequences, particularly regarding the absence of a testosterone flare.
Relugolix is marketed under two trade names for different indications. As Orgovyx, it is approved for advanced prostate cancer in adult men requiring androgen deprivation therapy. As Ryeqo, a combination product with estradiol and norethisterone acetate, it is approved for symptomatic uterine fibroids in premenopausal women. The oral route of administration offers a practical alternative to injectable GnRH agonists and injectable GnRH antagonists such as degarelix, which require depot injections every one to three months.
Mechanism of Action
Relugolix competitively and reversibly blocks GnRH receptors on gonadotroph cells of the anterior pituitary gland. Under normal physiological conditions, pulsatile GnRH release from the hypothalamus stimulates these receptors, causing pituitary release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). LH in turn stimulates testicular Leydig cells to produce testosterone. By blocking GnRH receptors, relugolix prevents LH and FSH secretion, thereby suppressing testosterone production and driving serum testosterone to castrate levels (below 50 ng/dL) within a few days of initiation. This rapid suppression contrasts sharply with GnRH agonists such as leuprolide or goserelin, which initially overstimulate GnRH receptors, triggering a transient testosterone surge (testosterone flare) that can temporarily worsen symptoms in patients with metastatic prostate cancer, including bone pain and spinal cord compression. Because relugolix acts as a competitive antagonist rather than an agonist, no initial testosterone flare occurs. After discontinuation of relugolix, testosterone levels recover more quickly than after injectable long-acting GnRH agonists, which may be clinically relevant in patients requiring intermittent androgen deprivation or those wishing to restore gonadal function. Relugolix is a substrate of P-glycoprotein (P-gp) and CYP3A4, and these transport and metabolic pathways are relevant to potential drug interactions.
Indications
In prostate cancer, relugolix (Orgovyx) is indicated for advanced hormone-sensitive prostate cancer in adults requiring androgen deprivation therapy (ADT). ADT is a cornerstone of treatment for locally advanced, metastatic, and biochemically recurrent prostate cancer, and relugolix provides an oral alternative to injectable forms of hormonal therapy. In the phase 3 HERO trial, relugolix demonstrated non-inferiority compared to leuprolide in achieving sustained testosterone suppression to castrate levels, with superior cardiovascular outcomes in a pre-specified subgroup analysis. For uterine fibroids, relugolix combined with estradiol and norethisterone acetate (Ryeqo) is indicated for the management of moderate-to-severe symptoms of uterine fibroids in premenopausal adult women. Relugolix induces temporary suppression of ovarian estrogen production, reducing fibroid size and associated symptoms such as heavy menstrual bleeding, pelvic pain, and pressure. The hormonal add-back component (estradiol and norethisterone) minimizes the hypoestrogenic side effects associated with relugolix monotherapy, including bone loss and menopausal symptoms.
Dosage and Administration
For prostate cancer (Orgovyx), the loading dose is 360 mg taken orally as a single dose on day one, followed by 120 mg once daily thereafter. The loading dose achieves rapid testosterone suppression within approximately 4 days. Tablets should be taken at approximately the same time each day and can be taken with or without food. For uterine fibroids (Ryeqo), the dose is one tablet containing relugolix 40 mg, estradiol 1 mg, and norethisterone acetate 0.5 mg, taken once daily. Treatment duration for uterine fibroids is typically limited to 24 months given the theoretical risk of bone density reduction over time, even with hormonal add-back therapy. Relugolix should be taken consistently, as irregular dosing may affect the degree and stability of sex hormone suppression. If a dose is missed, patients should take it as soon as possible within 12 hours of the scheduled time; if more than 12 hours have elapsed, the dose should be skipped and the regular schedule resumed.
Side Effects
The adverse effect profile of relugolix in prostate cancer reflects the consequences of castrate testosterone levels and is consistent with that of other androgen deprivation therapies. Hot flashes are the most common adverse effect, reported by the majority of patients. Fatigue, musculoskeletal pain, and weight changes are also frequently reported. Sexual side effects including decreased libido and erectile dysfunction are expected consequences of testosterone suppression. Long-term ADT is associated with reduction in bone mineral density, increasing the risk of osteoporosis and fractures; this should be monitored and managed with calcium, vitamin D supplementation, and bone-protective agents such as bisphosphonates when appropriate. Metabolic effects including dyslipidemia, insulin resistance, and increased cardiovascular risk are associated with ADT generally, though the HERO trial suggested a lower rate of major adverse cardiovascular events with relugolix compared to leuprolide in the first 48 weeks of therapy. For uterine fibroid treatment with Ryeqo, the hormonal add-back component substantially reduces hot flashes and bone loss compared to relugolix alone, making the combination considerably better tolerated.
Interactions
Relugolix is a substrate of both P-glycoprotein (P-gp) and CYP3A4, which creates important drug interaction concerns. Combined P-gp and CYP3A4 inducers such as rifampicin, carbamazepine, phenytoin, and St. John's Wort significantly reduce relugolix plasma concentrations, potentially leading to insufficient sex hormone suppression. Concurrent use with these agents should generally be avoided. Combined P-gp and CYP3A4 inhibitors such as itraconazole, ketoconazole, clarithromycin, and ritonavir can increase relugolix exposure, potentially enhancing side effects. For prostate cancer patients, alternative strategies to manage concurrent infections or other conditions should be considered when strong P-gp or CYP3A4 inhibitors are required. QT-prolonging drugs may interact with androgen deprivation therapy generally, as testosterone suppression itself can prolong the QT interval; concurrent use of drugs known to prolong QT requires monitoring. Antacids and drugs that significantly alter gastrointestinal motility may theoretically affect absorption, though relugolix is taken once daily and the clinical relevance of minor absorption changes is generally limited.
Special Notes
A key practical advantage of relugolix over injectable GnRH agonists is its oral route of administration, which eliminates the need for regular injections and allows for more flexible management of androgen deprivation therapy. In patients who require temporary interruption of ADT (e.g., for surgery or other clinical reasons), the rapid offset of action after stopping relugolix allows quicker testosterone recovery than with long-acting injectable GnRH agonists. Before prescribing relugolix for prostate cancer, the prescribing physician should review all concurrent medications for P-gp and CYP3A4 interaction potential. Bone density monitoring with DEXA scanning is recommended for patients on long-term ADT. Metabolic risk factors including blood glucose and lipid levels should be monitored regularly. For uterine fibroid treatment, the 24-month duration limit should be observed, and treatment decisions should include consideration of the patient's reproductive plans. Relugolix should not be used during pregnancy; in the Ryeqo formulation, hormonal contraception is not required as relugolix reliably suppresses ovulation, but non-hormonal contraception for pregnancy prevention is recommended if applicable.
Related Topics
Frequently Asked Questions
What is the testosterone flare and why does relugolix avoid it?
When GnRH agonists such as leuprolide are first administered, they initially overstimulate GnRH receptors before eventually causing receptor downregulation and sex hormone suppression. This initial overstimulation triggers a surge in LH and FSH, which briefly elevates testosterone levels above baseline, a phenomenon called testosterone flare. In men with metastatic prostate cancer, this flare can temporarily stimulate tumor growth and worsen symptoms such as bone pain or, in rare cases, precipitate spinal cord compression. Relugolix, as a competitive antagonist, directly blocks GnRH receptors from the first dose without any initial stimulation, meaning testosterone suppression begins within days and no flare occurs, which is a meaningful safety advantage in patients with high disease burden.
How quickly does testosterone recover after stopping relugolix?
Because relugolix is taken as a daily oral tablet and is competitively reversible at GnRH receptors, testosterone levels begin to recover relatively quickly after the last dose. In clinical studies, most patients showed recovery of testosterone to above castrate levels within 90 days of stopping relugolix, and a substantial proportion achieved recovery to normal physiological levels within this period. This compares favorably to injectable GnRH agonist depot formulations, which can suppress testosterone for 3 to 12 months after the last injection depending on the formulation. The faster reversibility of relugolix may benefit patients who experience significant quality-of-life impairment from testosterone suppression and those where treatment breaks are planned.
Can relugolix replace injectable androgen deprivation therapy in all patients?
Relugolix is a viable alternative to injectable ADT for most men with advanced prostate cancer requiring testosterone suppression. The main clinical considerations are drug interactions involving P-gp and CYP3A4, adherence to daily oral dosing (which is essential for maintained suppression), and the need for regular oral dosing without healthcare supervision. For patients on complex polypharmacy with strong P-gp or CYP3A4 inducers, injectable alternatives may be preferable to ensure reliable hormone suppression. For patients who prefer not to self-manage daily oral medication, or in settings where supervised administration is important, injectable options may still be appropriate. Shared decision-making between patient and oncologist is recommended.
Sources
- Shore ND et al. Oral Relugolix for Androgen-Deprivation Therapy in Advanced Prostate Cancer (HERO). N Engl J Med. 2020.
- EMA: Orgovyx (relugolix) Summary of Product Characteristics, current version.
- EMA: Ryeqo (relugolix/estradiol/norethisterone acetate) Summary of Product Characteristics, current version.