Description
What Is Zoladex?
Zoladex is a subcutaneous implant containing goserelin, a synthetic analogue of gonadotropin-releasing hormone (GnRH/LHRH). It is supplied in a pre-loaded single-use syringe that places a small biodegradable depot under the skin, releasing the drug slowly over time. The 3.6 mg implant is given every 28 days, while a 10.8 mg implant lasts about 12 weeks. Made by AstraZeneca, it is used to treat several hormone-sensitive conditions.
Zoladex is a prescription-only medicine used in men with prostate cancer and in women for breast cancer, endometriosis, uterine fibroids, endometrial thinning before surgery, and dysfunctional uterine bleeding. It works by lowering sex hormone levels, which slows the growth of hormone-dependent tumours and controls hormone-related gynaecological conditions.
Active Ingredient & Mechanism of Action
The active ingredient is goserelin (as goserelin acetate), a decapeptide GnRH agonist. It is not metabolised by CYP enzymes but broken down by peptide hydrolysis and cleared mainly in urine.
After an initial short-lived rise in luteinising hormone (LH) and testosterone (in men) or oestrogen (in women), continuous administration desensitises the pituitary, causing sustained suppression of gonadotropins. As a result, testosterone falls to castrate levels in men and oestrogen falls to post-menopausal levels in women, depriving hormone-dependent cancers and tissues of the hormones that drive their growth.
Approved Indications
In men, Zoladex is used for prostate cancer — locally advanced disease (including with radiotherapy or anti-androgens) and advanced/metastatic disease. In women, it is used for hormone-dependent advanced breast cancer, endometriosis, uterine fibroids (often before surgery), endometrial thinning before endometrial ablation, and to help protect the ovaries or manage bleeding in certain settings. The exact indication depends on the strength (3.6 mg or 10.8 mg) and the clinical situation.
Dosage & Administration
The usual dose is one 3.6 mg implant injected subcutaneously into the abdominal wall every 28 days. For prostate cancer, a 10.8 mg implant every 12 weeks may be used instead. Treatment duration depends on the condition: gynaecological uses such as endometriosis are usually limited (for example up to 6 months), while cancer treatment often continues long term. In men starting therapy for prostate cancer, an anti-androgen is often given around the first injection to cover the initial testosterone surge.
How Zoladex Is Given
Zoladex is administered by a doctor or nurse as a subcutaneous implant into the anterior abdominal wall, using the pre-loaded syringe device; it is not self-administered. The area may be numbed with local anaesthetic. After insertion the depot slowly releases goserelin until the next dose is due. Keeping to the scheduled 28-day (or 12-week) intervals is important to maintain hormone suppression. Attend all appointments so doses are not delayed.
Missed Dose
Because Zoladex is given by a healthcare professional on a fixed schedule, a missed or delayed implant should be arranged as soon as possible by contacting your clinic. Delays can allow hormone levels to rise again and reduce the treatment’s effect. Do not wait for the next planned date if a dose has been missed — ask your care team for advice on rescheduling.
Overdose
Overdose is unlikely given the fixed implant dosing administered by professionals, and there is limited experience. If an excess dose is inadvertently given, the patient should be monitored and treated symptomatically and supportively. There is no specific antidote; management focuses on observing for exaggerated hormonal effects.
Storage Conditions
Store Zoladex below 25°C; do not freeze. Keep the implant in its original sealed packaging until use to maintain sterility, and protect it from excessive heat. It is handled and stored by the clinic or pharmacy that administers it. Do not use after the expiry date, and dispose of the used device according to local requirements for medical sharps.
Contraindications
Zoladex is contraindicated in patients with known hypersensitivity to goserelin, other GnRH agonists, or any component. It is contraindicated in pregnancy and breastfeeding (the 3.6 mg gynaecological uses), and should not be used where pregnancy is possible without reliable contraception. Certain uses are specific to men or to women only, and the prescriber determines suitability based on the condition being treated.
Warnings & Precautions
A key early risk is the tumour “flare”: a temporary rise in hormones during the first weeks can briefly worsen cancer symptoms — in men this can cause ureteric obstruction or spinal cord compression and increased bone pain, so an anti-androgen is used to cover this period. Other precautions include reduced bone mineral density with long-term use, QT-interval prolongation and effects on heart rhythm, glucose and cardiovascular changes, mood changes, injection-site effects, and rare hypersensitivity or anaphylaxis.
Common & Serious Side Effects
Common effects reflect low sex hormones: hot flushes, sweating, reduced libido, and mood changes; in women also vaginal dryness, breast changes, and stopping of periods; in men, erectile dysfunction and breast tenderness. Injection-site reactions and headache are common. Serious effects requiring urgent attention include signs of spinal cord compression (leg weakness, numbness, bladder/bowel problems), severe bone pain, an irregular heartbeat, and symptoms of a severe allergic reaction.
Drug Interactions
Goserelin has few direct drug interactions because it is not metabolised by CYP enzymes. The main concern is with medicines that prolong the QT interval or affect heart rhythm, which should be used cautiously together. Combining LHRH agonists with anti-androgens is common and intentional in prostate cancer but may add to cardiovascular risk. Tell your doctor about all medicines you take so heart-rhythm and other risks can be reviewed.
Required Tests & Monitoring
Monitoring depends on the indication. In cancer, response is followed with PSA (prostate) or tumour assessment (breast) and testosterone or oestrogen levels where relevant. Bone mineral density may be checked with long-term use, and bone-protective measures considered. Blood glucose, lipids, and cardiovascular status should be monitored, along with heart rhythm (ECG) in those at risk of QT prolongation. Women’s ovarian suppression may be confirmed before certain therapies.
Diet & Lifestyle Support
Because Zoladex can reduce bone density, adequate calcium and vitamin D, weight-bearing exercise, and not smoking support bone health. A heart-healthy diet and activity help offset cardiovascular and metabolic effects of hormone suppression. Managing hot flushes and mood changes with your care team, and keeping to scheduled injections, all support treatment. Report new bone pain or neurological symptoms promptly.
Expected Timeline for Improvement
Hormone levels first rise briefly, then fall to castrate/post-menopausal levels within about 2 to 4 weeks. Cancer response is assessed over weeks to months through PSA or imaging; gynaecological symptoms such as endometriosis pain typically improve over the first months of treatment. The initial flare means symptoms may briefly worsen before improving. Your doctor assesses benefit at regular intervals and decides on the treatment duration.
Effect on Other Medications & Conditions
By lowering sex hormones, Zoladex can affect bone, cardiovascular, and metabolic health, so conditions such as osteoporosis, heart rhythm disorders, diabetes, and cardiovascular disease influence its use and monitoring. It is intentionally combined with anti-androgens in prostate cancer. All coexisting conditions and concurrent medicines — especially those affecting heart rhythm — should be reviewed by the prescriber before and during treatment.
When to See a Doctor
Seek urgent care for new leg weakness or numbness, difficulty passing urine, or severe back pain (possible spinal cord compression), for an irregular or very fast heartbeat, fainting, or for signs of a severe allergic reaction such as facial swelling, rash, or difficulty breathing. Contact your doctor about severe or worsening bone pain, persistent mood changes, or any new or concerning symptoms during treatment.
Use in Special Populations
Indications are sex-specific: prostate cancer in men; breast cancer and gynaecological conditions in women. Zoladex is contraindicated in pregnancy and breastfeeding for its gynaecological uses, and women of childbearing potential should use non-hormonal contraception during treatment. In older patients, bone and cardiovascular monitoring is important. It is not indicated for children. Care is needed in those with metabolic bone disease, heart rhythm disorders, or diabetes.
Who Should Avoid Zoladex?
Zoladex should be avoided by anyone hypersensitive to goserelin or other GnRH agonists, and in pregnancy or breastfeeding for its gynaecological indications. Particular caution applies in people with osteoporosis or risk of bone loss, heart rhythm disorders or QT prolongation, and significant cardiovascular disease or diabetes. In men at risk of tumour flare complications, it must be started with appropriate anti-androgen cover.
Frequently Asked Questions
What is Zoladex used for? Zoladex (goserelin) treats prostate cancer in men and breast cancer, endometriosis, fibroids, and other hormone-related conditions in women by lowering sex hormone levels.
How often is it given? The 3.6 mg implant is given under the skin every 28 days; a 10.8 mg implant for prostate cancer lasts about 12 weeks.
What is tumour flare? A brief early rise in hormones can temporarily worsen cancer symptoms; in men an anti-androgen is used to cover this period.
Does Zoladex affect the bones? Long-term use can reduce bone density, so calcium, vitamin D, exercise, and monitoring are advised.
Is it self-injected? No. It is given by a doctor or nurse as an implant into the abdominal wall.
Medical Review & Author Note
This page was medically reviewed by Dr. Abdallah Fouad, Clinical Nutrition Specialist with over 25 years of experience. The content is provided for educational purposes to help patients and caregivers understand how Zoladex (goserelin) is used, its benefits, and its risks. It does not replace the personalized advice of your treating physician or pharmacist.
Medical Disclaimer
Zoladex is a prescription-only medicine that must be prescribed and administered under the supervision of a qualified physician. This content is for general information only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your doctor or pharmacist before starting, changing, or stopping any medication.
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