Male Hormonal Contraception (MHC) Clinical Trials Network
Decades of research have now proven that MHCs are effective, reversible, and have minimal, tolerable side effects. We've known for decades that sperm creation can be stopped completely by giving men testosterone alone, but by adding progestins (a synthetic version of another naturally occurring sex hormone), methods become dramatically more effective. Contrary to popular belief, sperm counts don't have to go all the way down to zero to achieve contraceptive effectiveness. Once sperm counts are lowered to 1 million sperm/mL of ejaculate, pregnancy rates fall to levels below 1%, making MHCs as good as many female methods of contraception and far more effective than condoms. You might think that MHCs are going to take the form of "the pill" for men, but we're working on intramuscular injections, subcutaneous implants, and even topical gels!
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https://ctiexchange.org/giving-method-acceptability-research-due-contraceptive-development/