Goserelin, sold under the brand name Zoladex among others, is a medication which is used to suppress production of the sex hormones (testosterone and estrogen), particularly in the treatment of breast and prostate cancer. It is an injectable gonadotropin releasing hormone agonist (GnRH agonist). Structurally, it is a decapeptide. It is the natural GnRH decapeptide with two substitutions to inhibit rapid degradation. Goserelin stimulates the production of the sex hormones testosterone and estrogen in a non-pulsatile (non-physiological) manner. This causes the disruption of the endogenous hormonal feedback systems, resulting in the down-regulation of testosterone and estrogen production. It was patented in 1976 and approved for medical use in 1987. It is on the World Health Organization's List of Essential Medicines. Medical uses Goserelin is used to treat hormone-sensitive cancers of the breast (in pre- and peri-menopausal women) and prostate, and some benign gynaecological disorders (endometriosis, uterine fibroids and endometrial thinning). In addition, goserelin is used in assisted reproduction and in the treatment of precocious puberty. It may also be used in the treatment of male-to-female transgender people and is favoured above other anti-androgens in some countries, such as the UK. It is available as a 1-month depot and a long-acting 3-month depot. Goserelin is administered by subcutaneous injection as an implant every 28 days for the duration of treatment. Side effects Goserelin may cause a temporary increase in bone pain and symptoms of prostatic cancer during the first few weeks of treatment. This is known as the tumour flare effect, and is the result of an initial increase in luteinizing hormone production, before the receptors are desensitised and hormonal production is inhibited. The symptoms will disappear, with hormonal inhibition. It is therefore advisable to co-treat with an antiandrogen during the first 2–3 weeks of goserelin treatment, particularly in patients with pre-existing bone symptoms. Goserelin may cause bone pain, hot flushes, headache, stomach upset, depression, difficulty urinating (isolated cases), weight gain, swelling and tenderness of breasts (infrequent), decreased erections and reduced sexual desire. Bone pain can be managed symptomatically, and erectile dysfunction can be treated by vardenafil (Levitra) or other similar oral therapies, although they will not treat the reduced sexual desire. The rates of gynecomastia with goserelin have been found to range from 1 to 5%. Short-term memory impairment has also been reported in women and may in some cases be severe, but this effect disappears gradually once treatment is