The US Food and Drug Administration (FDA) on Thursday authorized Merck's Covid pill for high risk adults, a day after giving the green light to a similar pill by Pfizer.
"Today's authorization provides an additional treatment option against the COVID-19 virus in the form of a pill that can be taken orally," said FDA scientist Patrizia Cavazzoni.
The pill developed by Merck, which is known as MSD outside the US and Canada, is taken within five days of symptom onset and has been shown to reduce Covid hospitalizations and deaths by 30 percent among at-risk people.
Pfizer's pill reduced the same outcomes by 90 percent.
The FDA stressed in its statement that both the Pfizer and Merck pills should complement, rather than replace vaccines, that remain the frontline tool in the fight against the coronavirus.
While both treatments were found to be generally safe in clinical trials, more potential concerns have been raised about Merck's pill, called molnupiravir.
The FDA has not authorized Merck's pill for people under 18 because it may affect bone and cartilage growth.
It is not recommended for use in pregnant women because of the potential fetal harm, but doctors can still decide if the benefits outweigh the risks in individual cases.
Eight capsules of molnupiravir are taken orally for five days, for a total of 40 capsules.
The US has paid for 3.1 million courses of Merck's treatment, and 10 million courses of Pfizer's.
Molnupiravir works by incorporating itself into the genome of the virus, causing mutations that prevent viral replication.