hello,This decapeptyl reduce the reproductive hormones to low level and control reproductive environment from outside, which helps yoou to have proper hormonal environment to recive embryo. It is a long acting single dose injection which acts on the pituitary to reduce the production of FSH and LH hormones. Common side effects include --Pain, redness or inflammation of skin at the injection site.Hot flushes.Dizziness.Sweating.Headache.Decreased sex drive.Mood changes, including depression.Disturbances of the gut such as diarrhoea, constipation, nausea, vomiting or abdominal pain.Weight changes.Visual disturbances.Difficulty sleeping (insomnia).Excessive fluid retention in the body tissues, resulting in swelling (oedema).Pain in the muscles and joints.Increase in blood pressure.Decreased bone density.Vaginal dryness.Painful sex.Breast pain. they wont trouble much usually, but it deoends on individual.