BUDAPEST (Reuters) – Hungarian drugmaker Richter’s Esmya medicine used to treat benign tumors of the womb may have contributed to some cases of serious liver damage, European health regulators said on Friday after a months-long review.

The European Medicines Agency opened a review into Esmya, one of Richter’s flagship products, in late-November after reports of serious liver damage in patients treated with the drug.

The EMA’s specialist committee (PRAC) has recommended new measures to minimize risk of rare but serious liver injury.

“After considering all the evidence, the PRAC concluded that the medicine must not be used in women with liver problems and that certain other patients may start new treatment courses provided they have regular liver tests,” it said in a statement.

Richter, which has based its expansion into western Europe on female healthcare medicines, such as Esmya, declined to comment on the recommendation. It said the company would wait for the European Commission to deliver its final ruling.

The drugmaker has said it considered Esmya to be a safe and effective form of treatment. The investigation forced Richter in February to book an impairment loss and cut long-term sales targets for Esmya.

Shares in the company, which has a market capitalization of 1.1 trillion forints ($4.08 billion), fell sharply after the announcement. At 1251 GMT, the stock was down 3.1 percent at 5,645 forints.

The EMA said liver function tests should be performed before starting each treatment course and treatment must not begin if liver enzyme levels are more than twice the upper limit of normal.

“Esmya should be used for more than one treatment course only in women who are not eligible for surgery,” it said. “Women who are about to have surgery should continue to use only one course,” the EMA said.

The EMA also said new patients could start initial treatment with the product.

Esmya’s sales were 93 million euros last year, exceeding Richter’s forecasts.

Attila Vago, an analyst at brokerage Concorde, said uncertainty would weigh on Richter’s stock, which has lost nearly a fifth of its value in the past six months, until the Commission’s decision is published.

“It is hard to determine at this stage to what extent the new restrictions set back sales of the medicine,” he said. “But the product has not vanished from the market.”

The PRAC said the new restrictions would become applicable after a Commission decision is issued.

($1 = 269.36 forints)

(Reporting by Gergely Szakacs and Sandor Peto. Editing by Jane Merriman)