The widely prescribed drug for severe constipation, Zelnorm, is being taken off the market after it was linked to a higher risk of heart attacks and strokes, federal regulators said Friday.

Doctors said the voluntary withdrawal of Zelnorm by its manufacturer would leave few options for patients who suffer from a type of irritable bowel syndrome that affects about 12 million Americans, mostly women.

The Food and Drug Administration said it asked for the withdrawal of Zelnorm after an analysis of 29 studies involving more than 18,000 patients found that those who took the medication had significantly higher rates of cardiac problems than those who were given a sugar pill.

Patients taking Zelnorm should call their doctors to discuss alternative treatments, the agency said. Options include laxatives. Any patients who experience chest pain, sudden weakness or other symptoms of heart attack or stroke should immediately go to the emergency room.

The drug’s maker, Novartis, said it was complying with the FDA request but did not believe the drug was to blame.

A consultant who reviewed the data for the company said the rates of heart problems in patients taking Zelnorm roughly corresponded with the expected rates in the population.

Although the overall rates of problems were low — 0.1% for those taking Zelnorm, compared with 0.01% for those on a sugar pill — the disparity between the two groups got the FDA’s attention.

Zelnorm ranked among the top 200 brand-name prescriptions last year, according to the Internet site drugtopics.com, which monitors the drug industry.

More than 2.6 million prescriptions were written for the medication in 2006, a 25% increase from the previous year.