India has not added Merck's COVID-19 pill to its treatment protocol for the disease due to known safety concerns that have restricted its use elsewhere, a senior health official has told a media briefing.

"We have to remember that this drug has major safety concerns," Balram Bhargava, head of the state-run Indian Council of Medical Research, said.

"It can cause teratogenicity, mutagenicity and it also can cause cartilage damage and be damaging to muscles. More importantly, contraception will have to be used for three months if this drug is given because the child born could be problematic with teratogenic influences."

Teratogenic drugs can harm the development of a foetus while mutagenic ones can permanently change the genetic material of a person.

Merck and Indian drug maker Dr Reddy's Laboratories Ltd, which plans to launch a generic version of the pill early next week, did not immediately respond to requests for comment.

Drugs in the same class as Merck's pill, called molnupiravir, have been linked to birth defects in animal studies.

Merck has said similar studies of its drug - for longer and at higher doses than used in humans - show that it does not cause birth defects or cancer.

Bhargava said Indian health experts had twice deliberated on the Merck drug - which the country's regulators approved late last month and goes on sale on the private market from next week.

"The WHO has not included it, the UK has not included it as of now. As of now, the current recommendation stands that it is not part of the national taskforce treatment," he said.

The comments could hurt private sales of the drug when it hits the market as most doctors tend to follow recommendations from federal health officials.

The US FDA's Antimicrobial Drugs Advisory Committee voted 13-10 in November to recommend the drug after discussing concerns it could cause the virus to mutate as well as the potential birth defect worries.

Both FDA scientists and Merck have suggested the drug should not be recommended during pregnancy.

The UK in November was the first country to approve the pill but further trials are underway.