IVF Medications and Injections: The Drugs, How They Work, and Side Effects

IVF medications are the hormone drugs that control your cycle and grow several eggs at once, given mostly as injections you do yourself at home over about two weeks. They fall into a few clear groups, each with a job to do, and once you understand which drug does what, the daily routine of needles and timings feels far less daunting. For how these drugs fit into the wider process, see IVF explained.

The main groups of IVF drugs

IVF uses four drug groups in sequence: down-regulation, stimulation, a trigger shot, then progesterone support. Each targets a different part of the cycle, and your clinic chooses a protocol based on your age, your hormone levels, and how your ovaries are expected to respond. NICE guideline CG156 sets out the evidence-based approach UK clinics follow.

Down-regulation: pausing your natural cycle

Down-regulation drugs switch off your own hormone signals so the clinic can take control of timing. These are GnRH agonists (such as a daily nasal spray or injection) or GnRH antagonists (injections started later in the cycle). The point is to stop you ovulating early and releasing the eggs before collection. On a “long protocol” the agonist can start a couple of weeks before stimulation; antagonist protocols are shorter.

Stimulation: growing several eggs

Stimulation drugs are daily injections of follicle-stimulating hormone (FSH), sometimes with luteinising hormone (LH), that encourage the ovaries to ripen several eggs instead of the single egg of a natural month. This phase typically lasts around two weeks. You are monitored closely with ultrasound scans and blood tests, often every few days, so the dose can be adjusted to your response.

The trigger shot: ripening the eggs

The trigger injection gives the eggs their final maturation and sets the clock for collection. It is usually human chorionic gonadotrophin (hCG) or, in some protocols, a GnRH agonist, and the timing matters down to the hour. Egg collection is then booked for roughly 34 to 36 hours later. I set three phone alarms for my trigger shot; that single injection felt like the most important needle of the whole cycle.

Progesterone: supporting the womb lining

Progesterone support helps the lining of the womb become receptive to an embryo. It comes as vaginal pessaries or gel, or as intramuscular injections, and usually starts around the time of egg collection or transfer. If the cycle works, it often continues for several weeks into early pregnancy. This is the phase that runs through egg collection and embryo transfer.

How the injections actually work

Most IVF injections are subcutaneous, meaning they go into the fatty layer just under the skin of the tummy or thigh using a very fine needle. Many come as pre-filled pens, so you dial a dose rather than draw it up. Your fertility nurse teaches you the technique at a planning appointment, and a partner or relative can give them if you would rather not. Progesterone is the main exception: when given as an injection it is intramuscular, deeper, and can sting more. Rotating the site helps reduce bruising.

Common side effects

Most IVF medication side effects are mild and reflect the hormonal swings the drugs cause. Common ones include bloating, headaches, hot flushes, breast tenderness, mood changes, tiredness, and bruising or soreness where you inject. The NHS lists these as expected effects that usually settle once the cycle ends. They are uncomfortable rather than dangerous for most people, but tell your clinic about anything severe or unexpected. By the second week of stimulation I felt genuinely full and bloated, like my body had run out of room; my nurse had warned me, which made it reassuring rather than alarming.

OHSS: the warning signs to know

Ovarian hyperstimulation syndrome (OHSS) is the main serious risk of stimulation drugs, and it is the one to learn the signs for. It happens when the ovaries over-respond and fluid shifts in the body. Mild bloating is common and not a crisis, but contact your clinic urgently if you have severe or worsening tummy swelling and pain, rapid weight gain, breathlessness, persistent vomiting, or you are passing much less urine than usual. Severe OHSS is uncommon, but it needs prompt medical care, so do not wait it out at home. Clinics lower the risk by tailoring your dose, monitoring you closely, and sometimes adjusting the trigger or freezing all embryos for a later transfer.

Keeping the routine manageable

A clear system makes the daily injections far easier to live with. Keep your drugs stored as instructed (some need the fridge), lay out each day’s doses in advance, and write the timings somewhere you will see them. A simple checklist or phone alarms stop the “did I take it?” panic. If you ever miss a dose or are unsure, call your clinic rather than guessing, because timing is part of how these drugs work.

This guide is general information and support, not medical advice. Always follow your own clinic’s instructions, and consult your GP or fertility specialist about your medications and any symptoms that worry you.