IVF Medications Explained: What Each Drug Does

Almost every IVF medication belongs to one of four groups, each with a single clear job: grow the follicles, stop them releasing too early, mature the eggs at exactly the right moment, and support the uterine lining afterwards. Once you understand those four jobs, a bag full of unfamiliar boxes and syringes becomes a logical plan — this guide explains each group, why the choice matters, and what is normal versus what deserves a phone call.

The four jobs your medications do

An IVF cycle asks your body to mature many eggs at once, hold them until the ideal moment, and then hand control to the laboratory. The medication protocol mirrors that sequence:

1. Gonadotropins stimulate the ovaries so a group of follicles grows instead of just one.
2. GnRH agonists or antagonists prevent your brain from triggering ovulation before egg collection.
3. The trigger injection completes egg maturation roughly 36 hours before retrieval.
4. Luteal support — usually progesterone — keeps the uterine lining receptive after transfer.

Every protocol, however individual, is built from these building blocks. For how they fit into the two-week timeline, see our companion article on ovarian stimulation day by day.

Gonadotropins: growing the follicles

In a natural month, your pituitary gland releases follicle-stimulating hormone (FSH), and usually a single follicle wins the race to ovulation. Gonadotropin injections deliver FSH — sometimes combined with luteinising hormone (LH) activity — at higher, steady doses, so that the whole group of follicles recruited that month keeps growing rather than just one. You are not “using up” extra eggs: these follicles were already destined to be lost that cycle; stimulation simply rescues them.

Gonadotropins come as recombinant FSH or as purified urinary preparations containing both FSH and LH activity. Internationally you may hear brand names such as Gonal-F, Puregon, Menopur or Pergoveris; these are different formulations of the same underlying hormones, and evidence does not show one to be universally superior — your physician chooses based on your age, ovarian reserve and previous response, adjusting the dose according to ultrasound and blood results as the cycle progresses.

GnRH antagonists and agonists: preventing premature ovulation

As follicles grow, rising oestrogen would normally tell your brain to release an LH surge — the natural ovulation signal. If that happened mid-stimulation, the eggs would be released into the pelvis before collection and the cycle would be lost. Two families of drugs prevent this:

• GnRH antagonists (for example cetrorelix or ganirelix, sold as Cetrotide or Orgalutran) block the surge immediately. They are added as a daily injection from around day 5–6 of stimulation. This is the most widely used modern approach: shorter, fewer injections overall, and safer for women at risk of overstimulation.
• GnRH agonists (such as leuprolide or buserelin) work by “downregulation”: given for longer before stimulation starts, they first briefly stimulate and then exhaust the pituitary, switching off its signals. This is the classic “long protocol”, still chosen in selected situations.

Neither approach is inherently better for everyone; the choice reflects your ovarian reserve, diagnosis and history. ESHRE guidance on ovarian stimulation generally favours antagonist protocols for most patients, largely because of the safety advantage described next.

The trigger shot: hCG or agonist — and why it matters

Eggs collected straight from a stimulated follicle are not yet ready for fertilisation. The trigger injection, given at a precisely scheduled time about 36 hours before retrieval, completes their final maturation. There are two options, and the choice is one of the most important safety decisions in your cycle:

• hCG trigger (human chorionic gonadotropin, e.g. Ovitrelle) mimics the natural LH surge but lasts for days rather than hours. That long action supports the ovaries after retrieval — helpful for a fresh transfer — but in women with many follicles it is the main driver of ovarian hyperstimulation syndrome (OHSS).
• GnRH agonist trigger produces a short, natural-length surge and then switches off. It dramatically reduces OHSS risk, which is why it is preferred for high responders, including many women with polycystic ovaries. Because it withdraws hormonal support quickly, it is usually paired with freezing all embryos and transferring later — see fresh versus frozen embryo transfer for why this “freeze-all” strategy has become routine and does not reduce your chances.

If your clinic switches your planned trigger late in the cycle, this is almost always a safety decision based on your response, not a setback.

Luteal support: progesterone after transfer

Egg collection removes the cells that would normally produce progesterone, the hormone that keeps the uterine lining stable and receptive. Every IVF cycle therefore includes progesterone support, typically from retrieval until the pregnancy test and, if positive, for several more weeks. It comes in several forms — vaginal gels, pessaries or capsules, intramuscular injections, and in some protocols oral dydrogesterone. Studies comparing routes show broadly similar outcomes, so comfort and local practice guide the choice; vaginal leakage and mild discharge are normal and do not mean the dose is being lost.

Side effects: what is normal, and when to call

Usually normal: bruising or stinging at injection sites, bloating, breast tenderness, headaches, mood swings, tiredness, and mild pelvic heaviness as follicles grow. These reflect rising hormone levels — they are biology, not a sign anything is going wrong, and not a reflection of anything you did.

Call your clinic the same day if you notice:

• Rapidly increasing abdominal swelling or weight gain of more than about 1 kg per day
• Severe pelvic pain, persistent nausea or vomiting
• Shortness of breath, or urinating much less than usual
• Fever, or redness spreading from an injection site
• Heavy vaginal bleeding

The first three are warning signs of OHSS, which is uncommon with modern protocols but treatable and taken seriously — never “wait and see” at home. The HFEA publishes plain-language patient information on stimulation risks if you would like independent reading.

Injection practicalities and storage

• Most injections are subcutaneous — a short, fine needle into the fatty layer of the lower abdomen or thigh. Most patients find them far easier than feared after the first one or two.
• Timing: take stimulation injections at roughly the same time each evening; the trigger time, however, is exact to the minute — set two alarms.
• Storage: many gonadotropins and triggers need refrigeration (2–8 °C); check each box, and never freeze them. Most tolerate short periods at room temperature for travel — ask your nurse for your specific medicines. Use a cool bag for flights and carry medication in hand luggage with your prescription letter.
• Rotate sites a few centimetres each day to reduce bruising, and dispose of needles in the sharps container your clinic provides.
• Missed dose? Do not double up — call the clinic; almost every timing slip has a simple fix if reported promptly.

Understanding your medications will not change your protocol, but it changes how the cycle feels: fewer unknowns, fewer midnight worries, better questions at monitoring visits. For where each drug fits in the wider journey, see our IVF treatment guide.

Sources: ESHRE, HFEA, WHO and accepted reproductive-medicine guidance. This article is for general education and does not replace a medical consultation. Reviewed by Assist. Prof. Dr. Muzaffer Uçarer (Obstetrics & Gynaecology · IVF and Reproductive Medicine), UCARER Women’s Health, Istanbul.