The Food and Drug Administration is pulling its approval for a controversial drug that was intended to prevent premature births, but that studies showed wasn't effective.

Following years of back-and-forth between the agency and the drugmaker Covis Pharma, the FDA's decision came suddenly Thursday. It means the medication, Makena, and its generics are no longer approved drug products and can no longer "lawfully be distributed in interstate commerce," according to an agency statement.

"It is tragic that the scientific research and medical communities have not yet found a treatment shown to be effective in preventing preterm birth and improving neonatal outcomes," FDA Commissioner Robert M. Califf said in a statement on Thursday.

Hundreds of thousands of babies are born preterm every year in the U.S. It's one of the leading causes of infant deaths, according to a report released by the March of Dimes last year. And preterm birth rates are highest for Black infants compared to other racial and ethnic groups. There is no other approved treatment for preventing preterm birth.

Last month, Covis said it would pull Makena voluntarily, but it wanted that process to wind down over several months. On Thursday, the FDA rejected that proposal.

Makena was granted what's known as accelerated approval in 2011. Under accelerated approval, drugs can get on the market faster because their approvals are based on early data. But there's a catch: drugmakers need to do follow-up studies to confirm those drugs really work.

The results of studies later done on Makena were disappointing, so in 2020 the FDA recommended withdrawing the drug. But because Covis didn't voluntarily remove the drug at the time, a hearing was held in October – two years later – to discuss its potential withdrawal.

Ultimately, a panel of outside experts voted 14-1 to take the drug off the market.

But the FDA commissioner still needed to make a final decision.

In their decision to pull the drug immediately, Califf and chief scientist Namandjé Bumpus quoted one of the agency's advisors, Dr. Anjali Kaimal, an obstetrics and gynecology professor at the University of South Florida.

Kaimal said there should be another trial to test the drug's efficacy, but in the meantime, it doesn't make sense to give patients a medicine that doesn't appear to work: "Faced with that powerless feeling, is false hope really any hope at all?"