A new pill that aims to keep alcoholics from drinking again after they have quit could hit the shelves by the end of this year after U.S. health officials approved the drug on Thursday.

The drug, called Campral, may not work for people who are actively drinking when they start taking the pill or who are abusing other substances, the U.S. Food and Drug Administration said in a statement.

It was not clear how the pill worked, health officials said, but studies showed more patients who took the drug stayed away from drinking compared to those who took a placebo.

“While its mechanism of action is not fully understood, Campral is thought to act on the brain pathways related to alcohol abuse,” the FDA wrote.

Lipha Pharmaceuticals, a subsidiary of German drug maker Merck KGaA, makes the drug, generically known as acamprosate.

Forest Laboratories Inc. owns the licensing rights to sell the drug in the United States and plans to start selling it later this year, the company’s President and Chief Operating Officer Kenneth Goodman said in an interview.

The FDA had previously rejected the drug in 2002, asking Merck and Forest to conduct additional clinical trials.

Another company, Alkermes Inc., is in late-stage clinical trials to test its drug Vivitrex in alcoholic men. Other approved treatments, including the generics naltrexone and disulfiram, have been on the market for a number of years.

Alcoholism is a widespread problem in the United States. Last month, U.S. government researchers reported 17.6 million adults abused alcohol in 2001-2002. The National Institute on Alcohol Abuse and Alcoholism also found men and younger people aged 18 to 44 were more likely to drink heavily.

“Alcoholism, or alcohol dependence, is a disease ... that places a tremendous burden on society in terms of health care costs, lost wages and personal suffering,” the FDA said in its statement.

Common side effects from Campral, which has been widely used in Europe for 15 years, include diarrhea, nausea, vomiting and abdominal pain.