A contraceptive injection for men has been shown to be almost 100% effective - and may also increase libido. The hormone-based jab is designed to lower sperm counts by acting on the brain's pituitary gland. In a year-long trial 96% of couples relying on the jab to prevent unplanned pregnancies found it to be effective. Only four pregnancies occurred.Researchers said more work was needed to address the reported side effects: depression, mood disorders, muscle pain and acne. But the good news was that it increased libido.Mario Festin, from the World Health Organisation, said: "The study found it is possible to have a hormonal contraceptive for men that reduces the risk of unplanned pregnancies in the partners of men who use it."The injections contain a long-acting form of progestogen, a hormone that blocks sperm production controlled by the pituitary gland.Nearly 300 men were given injections every two months. At the end of the trial three-quarters said they would continue using the contraceptive jab. ..