Stocks of three Indian drugmakers surged and outperformed the sector amid speculation that an autoimmune and malaria therapy they produce could be effective to treat coronavirus.

U.S. President Donald Trump has been promoting the drug — hydroxychloroquine — since mid-March, stirring interest as healthcare professionals and governments around the world search for effective treatments for COVID-19, the disease caused by the novel coronavirus.

Because the drug is approved in the U.S. to treat malaria, lupus and rheumatoid arthritis, U.S. doctors can prescribe it off-label for other uses. On March 28, the U.S. Food and Drug Administration issued an emergency use authorization for doses of hydroxychloroquine in the federal stockpile to be used to treat hospitalized patients with coronavirus.

Meanwhile, the drug is undergoing clinical studies to test its safety and effectiveness in treating COVID-19.

To meet demand, India, one of the largest hydroxychloroquine manufacturers, lifted its ban on exporting the drug April 7. Explaining the decision in a post on its website, India's Ministry of External Affairs said the country's drugmakers should be able to meet export commitments as well as supply the domestic market.

Though the drug has not yet been approved to treat coronavirus, and experts have warned that side effects can include heart arrhythmias, investors have nonetheless bet on Indian manufacturers of the treatment.

Ahmedabad-based Cadila Healthcare Ltd. saw shares surge 39.1% this year as of April 11, surpassing the weighted average gain of 9.6% for 170 healthcare companies traded at the Indian stock exchange, according to data by S&P Global Market Intelligence.

Shares of Mumbai-based Ipca Laboratories Ltd. — which told the Bombay Stock Exchange on March 21 the company was "gearing to manufacture and supply" hydroxychloroquine — also saw its shares increase 36.6% during the period, while Cipla Ltd. stock jumped 24%.