Cetrotide is an injectable medication used during IVF to prevent premature ovulation, giving your fertility team control over exactly when your eggs are released. It works by blocking a hormone signal in your brain that would otherwise trigger ovulation too early, before your eggs are ready for retrieval. Within 8 hours of injection, it suppresses the two key reproductive hormones that drive the ovulation process.
How Cetrotide Works
Your brain naturally releases a signaling hormone called GnRH, which tells your pituitary gland to produce two hormones essential for ovulation: LH (luteinizing hormone) and FSH (follicle-stimulating hormone). During IVF, your doctor uses fertility medications to stimulate your ovaries into growing multiple eggs at once. The problem is that your body may detect all this activity and launch a premature LH surge, releasing those eggs before they can be collected.
Cetrotide (the brand name for cetrorelix) competes with GnRH for the same receptors on your pituitary gland. By occupying those receptors, it blocks the natural signal and rapidly suppresses both LH and FSH levels. This keeps your ovaries in a holding pattern, growing follicles and maturing eggs without releasing them, until your doctor triggers ovulation at exactly the right moment with an hCG injection.
When and How You Take It
Cetrotide is injected under the skin of your abdomen. You insert the needle straight in (not at an angle) after cleaning the area with an alcohol swab, and you should rotate injection sites each day to avoid irritation. Most IVF clinics prescribe one of two dosing approaches.
The more common protocol is a daily 0.25 mg injection starting on stimulation day 5 or 6 and continuing every 24 hours until the day you receive your trigger shot. This low daily dose is enough to maintain suppression around the clock.
The alternative is a single 3 mg injection, typically given around stimulation day 7 (though it can range from day 5 to 9 depending on your response). This larger dose provides at least 4 days of coverage. If your trigger shot hasn’t happened within those 4 days, you switch to daily 0.25 mg injections until it does.
Each Cetrotide kit comes as a powder in a small vial, a pre-filled syringe of sterile water for mixing, and two needles: a larger one for drawing up the solution and a finer one for the actual injection. Your clinic will walk you through the mixing process, which involves injecting the water into the vial, gently swirling until dissolved, then drawing the solution back into the syringe and switching to the smaller needle.
Side Effects
The most common side effect is a mild reaction at the injection site: redness, slight swelling, itching, or bruising. These reactions are typically short-lived and resolve on their own.
In clinical trials involving 949 patients, nausea occurred in about 1.3% of women. Moderate to severe ovarian hyperstimulation syndrome (OHSS), a condition where the ovaries swell and fluid leaks into the abdomen, was reported in 3.5% of patients. OHSS is a known risk of ovarian stimulation in general, not unique to Cetrotide. If your ovaries respond too aggressively to stimulation medications, your doctor may cancel the trigger shot entirely to reduce this risk.
Rare cases of allergic reactions, including serious hypersensitivity, have been reported after the drug reached the market, though these are uncommon.
How It Compares to Ganirelix
Ganirelix is the other widely used GnRH antagonist in IVF, and patients often wonder whether one works better than the other. A large retrospective study comparing 2,365 cetrorelix patients to 7,059 ganirelix patients found no meaningful difference in outcomes. Live birth rates were 47.2% with cetrorelix and 49.4% with ganirelix, a gap that was not statistically significant. Clinical pregnancy rates were similarly close: 54.8% versus 56.2%.
Cetrorelix did show tighter control over LH surges. The incidence of LH rising to problematic levels was 4.9% with cetrorelix compared to 7.6% with ganirelix. OHSS rates were also lower with cetrorelix (0.4% versus 1.1%). In frozen embryo transfer cycles, the two drugs performed almost identically, with live birth rates of 50.0% and 50.7% respectively. For practical purposes, the two medications are considered interchangeable, and your clinic’s choice often comes down to availability and protocol preference.
Why Timing Matters
Cetrotide is one piece of a carefully choreographed IVF cycle, and its timing is tied directly to how your follicles are developing. Starting it too early can over-suppress your hormones and slow follicle growth. Starting too late risks a premature LH surge that could cause you to ovulate before egg retrieval, potentially canceling the cycle.
If you miss a dose, contact your clinic immediately for guidance. Because the daily 0.25 mg dose is designed to maintain continuous suppression, even a short gap could allow LH levels to rise. Your clinic may adjust your schedule or monitor you with bloodwork to make sure suppression is still intact. Keep the medication refrigerated until you’re ready to use it, and set a daily alarm if you’re on the 0.25 mg protocol to help stay consistent.