Does Cetrotide need to be mixed before injecting?

Some presentations need reconstituting with the supplied diluent. Follow the leaflet in the box and your clinic nurse's guidance.

What happens if a dose is given at the wrong time?

Contact your clinic as soon as possible rather than trying to correct it yourself, since timing during stimulation is closely monitored.

Does it need to be refrigerated?

Storage instructions vary, so check the leaflet in the box for this specific product.

Why is it started partway through stimulation rather than from the start?

In an antagonist protocol it is added once follicles reach a certain stage, to prevent early ovulation at the point it becomes a risk. Your clinic will explain the exact plan for you.

GnRH antagonist injection

Cetrotide

Also known as Cetrorelix

Written by Zayn Miah & R KhanomLast updated 17 September 2026Not clinically reviewed

Cetrotide is a GnRH antagonist, given by injection under the skin, which works by blocking the natural hormone signal that would otherwise trigger early ovulation.

Why it may be used

It is used during IVF stimulation to prevent the body from releasing eggs too early, so that the eggs can continue developing until retrieval is planned by the clinic.

Where it fits in a cycle

It is usually introduced partway through the stimulation phase, once follicles have reached a certain size, and continues until the trigger injection is given. This forms part of what is often called an antagonist protocol.

Side effects listed in the patient leaflet

Injection site redness, itching or swelling
Headache
Nausea
Abdominal discomfort
Fatigue
Ovarian enlargement during treatment

When to ring the clinic

•Rapid or severe abdominal swelling
•Severe abdominal or pelvic pain
•Difficulty breathing
•Passing noticeably less urine
•Signs of infection at the injection site, or signs of an allergic reaction such as widespread rash or facial swelling

Questions people ask

Does Cetrotide need to be mixed before injecting?: Some presentations need reconstituting with the supplied diluent. Follow the leaflet in the box and your clinic nurse's guidance.
What happens if a dose is given at the wrong time?: Contact your clinic as soon as possible rather than trying to correct it yourself, since timing during stimulation is closely monitored.
Does it need to be refrigerated?: Storage instructions vary, so check the leaflet in the box for this specific product.
Why is it started partway through stimulation rather than from the start?: In an antagonist protocol it is added once follicles reach a certain stage, to prevent early ovulation at the point it becomes a risk. Your clinic will explain the exact plan for you.

Safety

This page is general information only, not medical advice, and does not replace your clinic's guidance.
Follow the specific schedule your clinic has set for you.
The patient information leaflet in the box is the authoritative source for this medicine.
Tell your clinic about other medicines, allergies and medical conditions before starting.

Sources

Patient information leaflets and product characteristics, electronic medicines compendium (emc). Link checked 17 September 2026.
IVF: what is IVF and how does it work?, HFEA (UK fertility regulator). Link checked 17 September 2026.

Written by patients, not clinicians. This page has not yet been reviewed by a named fertility professional, so it explains published guidance and points you to the original source instead of giving medical advice. It is not medical advice. Decisions about your treatment belong with your own clinic. Read our editorial policy and corrections policy.