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Study: Dietary Supplement To Boost Sexual Performance Often Mislabeled, Posing Risks

This article is more than 7 years old.

If you're not a man in the market for a natural way to boost your sexual performance, you may be unfamiliar with yohimbe. It's an African tree whose bark yields a substance, yohimbine, which can be extracted and used as an aphrodisiac.

But for those who seek this common supplement, beware: according to a new study by Harvard researchers, the vast majority of yohimbe sold as a dietary supplement by mainstream retailers in the U.S. is mislabeled in a way that could pose a safety risk to consumers.

Dr. Pieter Cohen, an assistant professor at Harvard Medical School who studies dietary supplements, says of the 49 yohimbe products he and his colleagues tested, most had inaccurate data either about the quantity of active ingredient or an incomplete list of known side effects.

"These are completely misleading in terms of labels," Cohen, the lead author of the new study and an internist at Cambridge Health Alliance, said in an interview. "If safe consumption of a product requires that both accurate quantity as well as known adverse effects be provided on the label, then only 4.1 percent of the yohimbine supplement brands analyzed provided sufficient safety information for consumers."

(Rachel Zimmerman/WBUR)
(Rachel Zimmerman/WBUR)

But the real problem, Cohen says, is the federal law governing dietary supplements which regulates such products more like food than drugs and doesn't require the kind of stringent pre-market testing for safety and effectiveness mandated for prescription drugs. "Every problem we found with yohimbe supplements brings us back to fundamental flaws in the law," Cohen said.

Here's the conclusion of his study, published today in the journal Drug Testing and Analysis:

The overwhelming majority of U.S. physicians no longer prescribe yohimbine. However, we found that pharmaceutical quantities of yohimbine are widely available in dietary supplements. While dietary supplements often contained pharmaceutically relevant quantities of yohimbine, the supplement labels very infrequently provide consumers with accurate information regarding quantity of yohimbine or known adverse effects... Our study demonstrates that consumers in the USA are unable to obtain adequate safety information from the overwhelming majority of yohimbine supplement brands offered for sale by seven mainstream retailers...This is a particularly concerning finding given that many countries have already banned yohimbine from all over-the-counter products due to its potential serious health effects.

Why should consumers care? Here, edited, is more of my conversation with Dr. Cohen.

RZ: Why did you focus on this particular dietary supplement?

PC: I became interested because my patients were taking these supplements and experiencing chest discomfort, flushing and I was worried that the supplements were spiked with prescription drugs. We had the supplements tested [at the National Center for Natural Products Research at the University of Mississippi]. Some had a lot of yohimbine [the active chemical that is extracted from the African yohimbe tree that's been used as a natural aphrodisiac].

It's illegal to sell yohimbe over-the-counter in Canada, Australia and several European countries, but in the U.S. you can sell yohimbe as a dietary supplement directly to consumers.
An extract of the bark has been used for years as an aphrodisiac. Scientists over 60 years ago started exploring which chemicals in the bark might be the most potent and eventually settled on yohimbine. Yohimbine was then developed as a prescription drug. But it doesn't really work very well — there are side effects, headaches, panic attacks, elevated blood pressure -- and it never became a popular prescription drug. Over the past 10 years, doctors have almost completely stopped writing prescriptions for yohimbine and most pharmaceutical firms have stopped making it. Doctors now use Viagra and similar drugs because these newer drugs are both more effective and safer than yohimbine.
So, we turned to yohimbe supplements because we were curious, were the contents more similar to simple extracts of tree bark or more similar to prescription drugs.
So the dose really does matter in this case?

Yes, 5 milligrams was the typical prescription dose of yohimbine.

What we found in the supplements we tested — which remember are what people go to when they want something natural -- were dosages much closer to the prescription dosages of yohimbine than the small amounts one would have expected from tree bark extract. We found in single servings up to 12 milligrams of yohimbine -- that is much higher than the prescription dose. We were surprised to learn that many of these over-the-counter supplements contained amounts of a drug higher than prescription doses.

What else did you find?

We were also interested to see if other natural components of the tree bark could be found in the supplements. What was shocking was that many of the products, 39 percent of them, did not contain two other compounds found in the bark. That tells us a lot. Either these products started with the plant and underwent a lot of processing to concentrate the yohimbine, or the yohimbine is being synthetically produced and marketed as the tree extract.

And why does that matter to Joe Consumer?

What matters is that the supplements are delivering prescription-level quantities of yohimbine. When drugs at prescription levels are sold as yohimbe supplements, the consumer has absolutely no idea how much drug they're getting. Only 22 percent of the supplements we tested listed specific quantity of yohimbine on the label. Of the ones that listed a quantity, only 3 of 11 were accurately labeled, and those three didn't contain the other compounds found in the tree bark.
So let's say you're having trouble with sexual function and you want to try something natural that has been used for hundreds of years to see if it helps. If you purchase these yohimbe supplements, you are much more likely to be using something similar to an old prescription drug with lots of side effects than a natural tree extract.

Why would manufacturers do this?

The law permits advertising for supplements: you can't say this will cure impotence, but you can say that this increases virility, stamina and desire. You can make all sorts of claims, and you don't need evidence that it works in humans. You can claim this botanical product has all these health benefits, so there's an incentive for supplement makers to do everything they can to make the product do something.

Any other findings of note?

Unfortunately, consumers can’t learn about the important side effects of yohimbine from reading these supplement labels. For example, yohimbine can cause headaches, hypertension and panic attacks. Nine out of the 49 we supplements we tested did not list any side effects at all.

Do you have any suggestions for fixing this?

Three things need to be changed in the laws regulating supplements:
1. There should be standard procedures used to prepare botanical supplements. Rather than allowing every manufacture to prepare their pills any way they choose, there should be standards, determined by a national standard setting organization, and all manufacturers should be required to follow the same manufacturing process. Only then will consumers buying yohimbe know what they were consuming.
2. Adverse effects should be required to be listed on the bottle.
3. The giant advertising loophole, called “structure/function claims” that permits false advertising, should be eliminated.
We should have access to high quality botanical supplements over the counter, but we should know what’s in the pills and powders we’re swallowing.

Rachel Zimmerman Twitter Reporter
Rachel Zimmerman previously reported on health and the intersection of health and business for WBUR. She is working on a memoir about rebuilding her family after her husband’s suicide. 



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