IVF Medications & Injections

An IVF cycle involves a sequence of medications, most of them self-injected. Each has a specific job:

Grow follicles – gonadotropins

In an unmedicated month, one follicle matures and the rest are left behind. During IVF, the stimulation phase uses medications to mature a batch of eggs for retrieval. They’re given as a daily subcutaneous injection, usually into the lower abdomen, for roughly 8 to 12 days.

Two hormones are at play. Follicle-stimulating hormone (FSH) is the primary driver: it directly stimulates the growth and recruitment of the ovarian follicles where eggs develop. Luteinizing hormone (LH) works alongside it, supporting follicle health, boosting estrogen production, and helping the eggs reach final maturation.

Gonal-F, Follistim, and Rekovelle are brand name recombinant FSH, made in a lab. Menopur carries both FSH and LH activity. Clinics choose among them, and often combine them, based on how a patient responded in a past cycle, or on ovarian reserve testing if it’s a first attempt. Patients are monitored with bloodwork and ultrasound every few days to track the response and the dose is adjusted accordingly. So dosage and duration vary from person to person.

Hold off ovulation – antagonist or agonist

Left alone, a body responds to rising hormones by releasing LH and ovulating. In IVF that would release the eggs before retrieval and the cycle would be lost. So a second drug holds that off. There are two ways to do it, and they behave differently.

Antagonists (Cetrotide generical called cetrorelix, and Fyremadel generic ganirelix) block the signal directly and work within hours. They’re started partway into stimulation, usually once the largest follicles pass about 12 to 14 millimeters. This is the more common approach with fewer injections, a shorter cycle, and a lower risk of OHSS.

Agonists (Lupron, generical leuprolide) work by first stimulating and then exhausting the pituitary gland — a tiny, pea-sized organ at the base of the brain that produces and releases hormones. This takes a week or more so it’s started before stimulation, sometimes in the cycle before.

Lupron seems to do two opposite things, but its effect depends on timing and dosage. Taken daily starting early in the process, it quiets the ovaries and keeps them from releasing eggs too soon. Given as a single large dose late in the process, it does the reverse and sets egg release in motion. Same molecule, opposite result, simply a matter of timing and dose. It’s why Lupron often shows up in two different places in an IVF protocol doing seemingly contradictory things.

Mature the egg – the trigger shot

When the follicles reach the right size (usually around 16 – 22 millimeters), one carefully timed injection finishes the eggs’ maturation. This trigger shot is given about 36 hours before egg retrieval, and the timing is exact because retrieval has to happen in the window after the eggs mature but before the body releases them. Miss the trigger or mistime it and the cycle can be lost, so clinics give very specific instructions down to the minute.

• hCG triggers (Ovidrel, Pregnyl, Novarel) mimic the natural LH surge. hCG stays in the system for days, which is what makes it useful but also what raises risk of ovarian hyperstimulation syndrome (OHSS).
• A GnRH agonist trigger (a high dose of Lupron) produces a shorter surge and substantially lowers OHSS risk. It only works if an antagonist was used during stimulation, and it usually requires freezing all embryos rather than transferring fresh.

This is a real fork in the protocol. Choosing an agonist trigger for OHSS safety generally means no fresh transfer, so the embryos are frozen and transferred in a later cycle. That decision gets made before the trigger, not after.

Prepare the uterus – progesterone

Progesterone helps to create a receptive environment for embryo implantation. In a fresh transfer cycle, egg retrieval disrupts the body’s own production of progesterone. In a frozen cycle there’s no ovulation at all, so there’s no natural production to begin with. Either way it has to be supplied.

The progesterone medication comes two ways. Vaginal, as an insert (Endometrin) or gel (Crinone), and intramuscular, as progesterone in oil, often shortened to PIO. Oral progesterone is absorbed too poorly to rely on.

Fresh transfers apply to cycles that used an hCG trigger. If you had an agonist trigger, you’re almost certainly doing a frozen transfer.

For fresh transfers, studies have shown that both routes work equally well, with no meaningful difference in pregnancy or live birth.

For frozen transfers, the evidence is a little less clear-cut. One randomized trial of 1,060 transfers found a live birth rate of 27% with vaginal alone against 44% with injection. But a systematic review of 15 randomized trials covering 5,656 patients found no significant difference between the two routes, including when frozen and fresh cycles were analyzed separately. It also found patients significantly preferred the vaginal route. Practice differs by geography more than by evidence: injections have been the default in the US and vaginal in Europe.

Progesterone medication usually continues until the placenta takes over its production, around 8 to 10 weeks of pregnancy. In fresh cycles, the ovaries are still producing some progesterone on their own, so some clinics stop earlier, sometimes as soon as a positive pregnancy test.

Some protocols add estrogen, mainly in frozen transfers, to build the uterine lining before progesterone starts. It’s a tablet (usually Estrace) or a patch (Vivelle-Dot, Climara) rather than an injection.

A typical timeline of IVF meds

The volume is what surprises people most. A typical antagonist cycle runs 1-3 shots a day for about 10 days, then the trigger shot, then daily progesterone for weeks after the embryo transfer. A few injections are time-sensitive to the hour. Following the pharmacy’s and clinic’s instructions on each matters more here than with everyday medications.

The injections themselves

There are two kinds of shots you give yourself during IVF, either in prefilled pens or vials you draw from yourself.

Stimulation drugs, antagonists, and most triggers are subcutaneous: a short, fine needle into the fatty tissue of the belly or thigh, which most people manage at home after a nurse walkthrough.

Progesterone in oil is intramuscular: a longer needle into the upper outer buttock, usually given by a partner.

Side effects

Most side effects are mild and pass when the cycle ends: bloating, breast or abdominal tenderness as the ovaries enlarge, bruising or redness at injection sites, headaches, fatigue, and mood changes. Progesterone tends to also bring drowsiness and bloating, and its side effects overlap almost exactly with early pregnancy symptoms, which makes the two-week wait even harder than people expect.

Ovarian hyperstimulation syndrome (OHSS) is a side effect to watch for. It’s an over-response to the medications with symptoms of rapid weight gain, severe bloating, shortness of breath, or reduced urination after retrieval. It can either be just uncomfortable or can cause serious complications. Our Risks of IVF post covers OHSS in detail.

Key takeaway

IVF medications are a coordinated sequence, mostly self-injected, each doing one job:

• gonadotropins grow the eggs
• antagonist or agonist holds off ovulation
• trigger matures eggs on schedule
• progesterone prepares the uterus

Your exact medication, dosage, and protocol are tailored to your age, ovarian reserve, how you respond, and OHSS risk.

Sources

• American Society for Reproductive Medicine, “Use of Exogenous Gonadotropins for Ovulation Induction in Anovulatory Women: a Committee Opinion” (2020)
• American Society for Reproductive Medicine, “Medications for Inducing Ovulation”
• American Society for Reproductive Medicine, “Progesterone Supplementation During the Luteal Phase and in Early Pregnancy in the Treatment of Infertility”
• American Society for Reproductive Medicine, “Prevention and Treatment of Moderate and Severe Ovarian Hyperstimulation Syndrome: a Guideline”
• Fertility and Sterility, “Matched-samples comparison of intramuscular versus vaginal progesterone for luteal phase support after in vitro fertilization and embryo transfer” (2009)
• Fertility and Sterility, “Intramuscular progesterone optimizes live birth from programmed frozen embryo transfer: a randomized clinical trial” (2021)
• Gynecological Endocrinology, “Vaginal versus intramuscular progesterone for luteal phase support in assisted reproductive techniques: a systematic review and meta-analysis of randomized controlled trials” (2020)