A Web site advertising “Canadian generic” drugs shipped fake, contaminated or substandard versions of three commonly prescribed medicines, U.S. regulators said on Tuesday.

Food and Drug Administration investigators ordered generic versions of Pfizer Inc.‘s impotence pill Viagra and cholesterol-fighter Lipitor, as well as Sanofi-Synthelabo’s sleeping pill Ambien.

The Web site “shipped drugs that were the wrong strength, including some that were substantially super-potent and that pose real health risks as a result,” Acting Food and Drug Administration Commissioner Lester Crawford said.

Some of the pills were drugs that “contained contaminants” or should not have been given because of potentially dangerous interactions with other medicines, Crawford added.

The FDA did not identify the Web site but said it had been sending “spam” e-mail to consumers touting its products.

Despite frequent government warnings about safety risks, buying cheaper drugs online is a growing trend as drug costs rise and more Americans lose health insurance.

Advocates of drug importation say the FDA is exaggerating risks, particularly for medicines bought in Canada. Congress is considering legislation to set up a legal system for importing prescription drugs from certain countries.

The FDA said its recent purchases showed consumers can be misled “even where a Web site looks legitimate.”

The pills sold as copies of Ambien had too much active ingredient. One tablet was nearly twice the normal strength, the FDA said.

The Lipitor copies on average contained 57 percent of the amount of active ingredient listed on the label. The Viagra copycats also were subpotent, the FDA said.

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