Researchers have been looking at ways to develop a form of birth control for men for over 20 years, and a new study has found a method that is quite effective, but comes with a number of undesirable side effects, according to bbc.com.

The method involves regular injections, containing high levels of hormones, that reduce the levels of normal sperm from a whopping 15 million per milliliter to under one million/ml.

Researchers selected a group of some 270 males between the ages of 18 and 45 for the trial.  Each of the men reported they had been in a monogamous relationship for at least a year, and their partners agreed to take part in the survey.

After an initial sperm count check to verify the men were normal, the subjects were injected with two hormones twice weekly for eight weeks, and were monitored for as much as six months, until their sperm count fell below the one million/ml mark.

The men were tasked with relying on the injections as their sole form of birth control, while continuing to receive the injections at the same rate for a period of one year.

At the end of the injections, the men were monitored to see how long it took for the men’s sperm count to return to normal.  Eight of the participants still had not recovered to a normal sperm count within a year from the cessation of the injections.

The method produced a 96 percent effective rate, with four pregnancies recorded during the study.  Unfortunately, a relative large number of participants experienced side effects from the injections, including developing acne, suffering from mood disorders, and experiencing muscle pain.  Twenty of the participants dropped out of the study due to the side effects.

“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,” according to Dr. Mario Festin of the World Health Organization.

The researchers say because the study was so effective, they are looking at different combinations and levels of the hormones, and different method of delivery, and noted that despite the side effects, three-quarters of the men in  the study said they would be willing to use this method of contraception again.

Findings from the research were published in the Journal of Clinical Endocrinology & Metabolism.