The second pill for Covid should not be a preferred treatment according to the FDA.
The F.D.A. cleared the pill for adults who are vulnerable to becoming severely ill from Covid and for whom alternative Covid treatment options are not accessible.
Older people and people with certain conditions who can't get the same pills from Pfizer, for example, would be able to get a prescription for them.
The treatment is expected to be available within a few weeks.
Concerns about the risk of reproductive harm have been raised by the fact that the pill works by introducing errors into the virus's genes. The F.D.A. said that if the woman and her health care provider discuss the risks and benefits, there could be exceptions. The F.D.A. said that women who may become pregnant should use contraception while taking the pills and for at least four days after. The male partners of women who could become pregnant should use contraceptives for at least three months after the baby is born.
Before the F.D.A.'s ome doctors and health officials have tempers for the drug. It is less effective than Pfizer's version, which received F.D.A. authorization on Wednesday and is expected to become more widely available in the United States starting in a few months.
Dr. Walid Gellad, director of the Center for Pharmaceutical Policy and Prescribing at the University of Pittsburgh, doesn't think the new version from Merck will be a game-changer.
The drug can stop the Omicron variant from replicating, but it is not known how well it works. Scientists are optimistic that the drug will work against Omicron.
The pills from the two companies can be taken at home and are expected to reach many more people than the treatments that are typically given by a health care provider.
Until this week, the only authorized treatment options for Covid patients who are at high risk of becoming severely ill were the antibody drugs. The country has a shortage of the antibodies. Several of the antibody drugs have been stopped by some hospitals because they are not likely to work against Omicron, and the only potent treatment remaining is in very limited supply.
When given to high-risk unvaccinated people within five days of the start of symptoms, the drug reduced the risk of hospitalization or death by 30 percent. The Pfizer pill reduced that risk by 88 percent.
Pfizer's treatment is expected to be in greater supply sooner. By the end of January, the federal government is expected to have enough pills for 3.1 million people at a cost of $700 a person. About two weeks after authorization, the first 378,000 treatment courses are expected.
Paxlovid is expected to be available before the end of January for 265,000 people. Supplies are expected to arrive in the next few days.
The F.D.A. said that patients will need to test positive for the virus and get a prescription from a health care provider if they start having symptoms.
The F.D.A. didn't specify which type of test was used, opening the door for over-the-counter rapid antigen tests, which return results within 15 minutes. The 500 million rapid tests that President Biden plans to give out to the public may not be enough to meet the high demand.
