The government overturns a 30-year policy banning gay men from giving blood donations

Thomson ReutersPeople line up to give blood at a mobile donation station set up following the shooting at Umpqua Community College in Roseburg

For the first time in 30 years, gay men in the US are allowed to give blood - but there's an important caveat.

The US Food and Drug Administration on Monday finalized a rule that will allow gay men to donate blood 12 months after their last sexual contact with another man.

This overturned a 30-year policy in which men who had sex with men could not donate blood no matter how long they were abstinent.

"Ultimately, the 12-month deferral window is supported by the best available scientific evidence, at this point in time, relevant to the U.S. population," Dr. Peter Marks, deputy director of the FDA's biologics division, said in a statement.

Several countries, including the United Kingdom and Australia, have 12-month deferrals.

The ban originally was in place to reduce the spread of HIV, of which men who have sex with men are more severely affected, according to the Centers for Disease Control and Prevention.

Reuters reporting by Toni Clarke in Washington.