The ephedra effect

Editor's note: CNN's Dr. Sanjay Gupta answers medical questions submitted by e-mail on "Your Health," which airs at 2:30 p.m. ET Saturdays. Questions and answers are posted on CNN.com after the show.

Q: What are the negative effects of ephedra and can they be reversed? -- Gwen from Farwell, Texas

A: Ephedra is a stimulant.

In many herbal products it is combined with caffeine and aspirin to produce thermogenesis.

That means it increases the body's ability to produce heat and burn stored calories.

It does this by increasing your blood pressure and your heart rate.

It has also been linked to anxiety, insomnia and dehydration -- and in some extreme cases -- even psychosis.

These symptoms usually disappear once you stop taking ephedra.

You should talk with your doctor before taking any herbal supplement.

Q: What are the pros and cons of diet pills -- and do they work? -- Frances from Gatesville, North Carolina

A: The answer to this question is as varied as the number of products on the market.

Over-the-counter diet pills often contain ephedrine, which is the active ingredient in ephedra. We just talked about that.

Others may contain a combination of apple cider vinegar, kelp, vitamin B-6 and lecithin. This has been called a miracle cure for weight-loss.

There's no scientific material to support this claim.

Prescription diet pills can contain amphetamines, which stimulate the central nervous system.

They may increase your physical and mental activity for a while, but prolonged use can be dangerous.

Before you begin any weight-loss plan, check with your doctor.

"Ask Dr. Gupta" is not intended to address specific questions concerning individual cases. CNN does not directly or indirectly practice medicine or provide medical advice, and nothing contained in the responses of CNN through its correspondents is a substitute for medical advice, diagnosis or treatment. Always contact your doctor if you need medical advice or treatment, or have any questions regarding a medical condition.