Ganirelix is a synthetic third generation gonadotropin-releasing hormone (GnRH) antagonist that is administered via the subcutaneous route. The drug competitively blocks GnRH receptors in the anterior pituitary gland, preventing endogenous GnRH from inducing luteinising hormone (LH) and follicle stimulating hormone release. Ganirelix effectively inhibited LH surges during controlled ovarian stimulation in a large, multicentre clinical trial in women undergoing in vitro fertilisation. A vital pregnancy rate per embryo transfer of 40.3% was achieved at weeks 5 to 6 after treatment with the 0.25 mg/day dosage. Subcutaneous ganirelix has been generally well tolerated in clinical trials. The most common adverse events were local injection site events, asthenia, nausea, malaise, headache and fatigue.