Pharmaceutical giant Merck said Friday that its COVID-19 pill could be less effective than originally thought.
The drugmaker said the experimental pill, molnupiravir, was shown to be 30 percent effective in fighting hospitalizations and deaths in a study of 1,433 patients.
That’s a drop from a 50 percent effectiveness rate in a prior study of 775 patients.
By contrast, a Pfizer COVID-19 pill showed an 89-percent efficacy rate among 1,200 patients who took their drug, paxlovid.
Friday’s announcement drove stock prices down by 3.9 percent to $79.12 in afternoon trading.
Merck released their latest results as the Food and Drug Administration considers approving the pill.
The FDA has said molnupiravir is effective in combating serious COVID-19 illness and death, but that they want to vet it for birth defect and pregnancy risks.
The agency said Merck agreed not to make the pill available to children.
Officials have said that anti-COVID-19 pills can help to fight the virus in its early stages and can be especially useful in areas with limited vaccine availability.
If regulators approve the pills, they could soon become the first drug COVID-19 patients can administer from home.