How should I counsel a patient regarding the effectiveness and potential side effects of the progestogen-only injection?

Effectiveness: The progestogen-only injectable is a highly effective contraceptive method when administered every 13 weeks, with a small window for late injection up to 7 days (or 14 weeks off-label for intramuscular DMPA). It is important to advise the patient to return on time for repeat injections to maintain contraceptive efficacy.

Potential Side Effects: Common side effects include menstrual irregularities such as amenorrhoea, infrequent bleeding, spotting, and prolonged bleeding, which tend to improve with continued use. Weight gain is frequently reported and can be a reason for discontinuation, especially in women with a higher initial BMI. Other possible side effects listed in product information include depression and mood changes, decreased libido, acne, headache, hot flushes, and vaginal infections or vaginitis, although evidence for a causal link is limited.

Bone Mineral Density (BMD): Long-term use (over 1 year) is associated with a small loss of BMD, which usually recovers after stopping the injection. Women using the injectable long term should be reviewed every 2 years to assess risks and benefits, especially those under 18 or with risk factors for osteoporosis.

Cancer and Cardiovascular Risks: There is possibly a weak association between current use and breast cancer, and a weak association with cervical cancer after 5 years or more of use, but risks reduce after stopping. No causal association with venous thrombosis has been demonstrated. The association with myocardial infarction or stroke is not confirmed or excluded.

Additional Advice: Women should be advised to seek medical advice if they experience mood changes or depressive symptoms. Injection site reactions may occur, more commonly with subcutaneous administration. The progestogen-only injectable may reduce the effectiveness of ulipristal acetate emergency contraception.