A ban on codeine-based cough syrups of the Indian units of US-based drugmakers Pfizer and Abbott Laboratories has resulted in the shares of these companies falling by as much as 5% on Monday.

The ban was slapped by Indian authorities claiming codeine, a narcotic, posed a health risk. While Pfizer's India unit sells the product by the name Corex, Abbott does so by the brand name Phensedyl. Pfizer said it had already suspended the sale of Corex even as Abbott did not respond to a request for comment.

These syrups contain a combination of chlopheniramine maleate and codeine which, a government panel of experts said, had “no therapeutic justification.” The drugs were among 344 drug combinations banned by India over the weekend.

Indian authorities said the banned drugs had entered the market over the years following a green signal from regulators of individual states instead of a go-ahead from the central government, something that is legally binding.

Pfizer said in a statement that the brand Corex brought in sales of about 1.76 billion rupees ($26.29 million) in the third quarter ended December 2015. Phensedyl governs over one-third of the Indian cough syrup market and its sales make up for more than 3% of Abbott's $1 billion India revenue. Abbott India Ltd's shares fell nearly 3% while that of Pfizer Ltd declined by 5.2% in early Indian trade on Monday.

India had set up a committee in 2014 to review more than 6,000 combinations that had forayed into the market only on the basis of approval from state regulators. KL Sharma, a joint secretary at the health ministry, said the committee was tasked with classifying the drugs into rational, irrational, and those that need further studies. “Now based on responses (and) assessment of products, more than 300 drugs have been prohibited”, he said.