An over-the-counter diet pill approved by the U.S. Food and Drug Administration hits store shelves Friday, but some doctors are questioning if its benefits are worth its costs.

The over-the-counter drug orlistat, sold in the U.S. as Alli, comes in 60 milligram pills, half that of the prescription version, which has been available in Canada for a few years.

In a three-month trial, people lost an average of 2.7 kilograms when taking the drug, but many gained it back after they stopped taking it. It is not intended for long-term use.

The drug works by blocking the absorption of fat in the colon, so about 30 per cent of fat is excreted.

But the drug has unpleasant side-effects such as diarrhea, leakage, bloating and oily discharge that may help stave off abuse, said Dr. Dara Maker, a family physician in Toronto.

The drug also leads to poor absorption, so multivitamins are recommended for people who take it.

Alli tablets may be taken three times a day, adding up to a cost of about $50 US a month. Canadian drug plans do not cover it, said Dr. Mike Evans, a family physician in Toronto.

Evans said he is also concerned about teens taking the drugs, since there have been few studies on the use of orlistat among that age group. The FDA approved it for people 18 and older.

The question is, how many people will find Alli's benefits worth the cost, asked Dr. Kelly Brownell, a food policy researcher at Yale University.

People may also not lose as much weight as they hoped and stop taking the drug, Brownell added. Doctors have seen that happen with the prescription version.

In its marketing plan, the drug's manufacturer, GlaxoSmithKline, emphasizes Alli needs to be taken along with diet and exercise.

The FDA approved Alli for use in combination with a reduced-calorie, low-fat diet and exercise program.

With files from the Associated Press