The Food and Drug Administration (FDA) says that while Merck's experimental COVID-19 antiviral pill is effective, the agency has yet to determine whether the medication can be safely administered during pregnancy.
The FDA said a review identified several potential risks, including possible toxicity and birth defects, The Associated Press reported on Friday.
Advisers and experts will gather at a public meeting Tuesday to discuss concerns, and that Merck has agreed the drug would not be used in children, per AP.
The FDA says the drug, called molnupiravir, will carry a warning about risks of use during pregnancy, but it could still be prescribed by doctors if the benefits are believed to outweigh the potential for danger.
Merck acknowledged on Friday that updated data shows molnupiravir is significantly less effective in cutting hospitalizations and deaths than previously reported, Reuters reported.
The company said its pill showed a 30 percent reduction in hospitalizations and deaths, based on data from 1,433 patients. In October, the data showed a roughly 50 percent efficacy, based on data from 775 patients, Reuters added.
Molnupiravir, which is administered as a five-day treatment and was developed in association with Ridgeback Biotherapeutics, targets the enzyme that allows the coronavirus to make copies of itself. Officials say it is likely to be effective against COVID-19 variants, including the highly infectious delta variant.
The FDA has also asked for expert comment on concerns over whether the drug could encourage the virus to mutate and create new strains, as well as how those concerns could be mitigated.
Molnupiravir has been touted as a "game changer" with regards to the pandemic.
Former FDA Commissioner Scott Gottlieb has predicted that the "pandemic phase" of the coronavirus would likely come to an end with the approval of antiviral pills as well as the approval of COVID-19 vaccines for children under 12.
Merck requested FDA authorization for the pill last month.