U.S. health authorities warned consumers recently about the dangers of so-called herbal Viagra - non-prescription products sold to enhance sexual performance - reportedly used by former NBA star Lamar Odom, who is in critical condition in a Nevada hospital.

Entertainment website TMZ.com reported Odom was on life support after collapsing in a legal brothel in Nevada on Tuesday. Brothel owner Dennis Hof said in an email that staff there had reported Odom was taking herbal sexual enhancement capsules.

The hospital has not commented on Odom's condition, and the cause of his collapse is not known. It is unclear whether these supplements alone could have caused the condition. Odom has not publicly discussed any drug use other than marijuana. He was suspended during the 2000-01 season for violating the NBA's anti-drug policy for the second time in eight months, but the NBA will not say what drug was involved.

Dozens of supplements are sold both online and in retail establishments and touted as natural or herbal versions of prescription drugs used to treat erectile dysfunction, the Food and Drug Administration said in a consumer update released on Oct. 1.

Powders and herbs promising vigor, stamina and virility often claim to contain natural ingredients such as horny goat weed.

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The update warned that products falsely marketed as "dietary supplements" that promise to enhance sexual performance are "a risky proposition."

"We're finding an alarming number of these products sold online and in retail stores," said Gary Coody, FDA's national health fraud coordinator in the report, adding they are often sold in single-serving sizes in gas stations or vending machines.

"We've seen pills, coffees, chewing gum and dissolvable oral strips that contain hidden drug ingredients or untested chemicals," he said.

The consumer warning said the big risk is that the products often contain drug ingredients that could interact dangerously with heart disease medicines or other prescription drugs.

Taking a product that contains sildenafil, the active ingredient in Viagra, along with certain drugs containing nitrates may lower blood pressure to an unsafe level, the FDA said in the consumer warning.