Well, this is a half-truth, although the answer currently is yes: gay men can become sperm donors as well as heterosexual males.
We say half-truth because, 6 years ago, the FDA in the United States had a rule by which gay men were precluded from donating sperm if the candidate admitted to having had sex with another man over the past 5 years. The rule is included within Title 21, Chapter 1, Subchapter L, Part 1271 of the Code of Federal Regulations.
Today, every donor, regardless of his sexual orientation, must be screened for HIV and other STDs, and the tests available are 99% effective.
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