What's Really in Your Diet Pill?

“Dietary supplements may represent the next big drug-safety catastrophe,” says Dr Steven Nissen, a cardiologist at the Cleveland Clinic and a US Prevention advisory-board member. “We don’t know exactly what most supplements contain, so we don’t know whether they’re actually safe.” More and more, manufacturers of weight-loss products are polluting them (along with supplements that claim to treat sexual dysfunction or enhance athletic performance) with potentially dangerous ingredients.

MORE: Diet Pills: Doing More Harm than Good?

Originally, the makers would include something like caffeine to give it a kick, but now they’re adding compounds you find in prescription drugs without including that information on their labels. Some of these products—which are usually sold on the internet so manufacturers can evade regulators—may include versions of Reductil (or Meridia) and erectile-dysfunction drugs, such as Viagra, Cialis or Levitra, without consumers’ knowledge.

The other thing consumers don’t realise is that adulterated products can be far riskier than prescription diet pills. If you’d had a prescription for, say, Reductil before the TGA banned it, you would have been under a doctor’s care. You would have been aware of how much sibutramine you were taking, as well as what side effects you could expect, because they were listed on the label. But in the more or less unregulated world of weight-loss supplements, there’s no way to definitively know what or how much you’re getting—or what it can do to you.

In recent years, the TGA has gone after many tainted weight-loss products. The administration has found that a number of these were laced with undeclared stimulants, chemical laxatives and antidepressants, often in amounts exceeding the maximum recommended dosages at which such drugs can be prescribed.

Even so, there are still dangerous pills out there. For example, one supplement that’s available online (and whose makers ship to Australia) contains fenproporex, a stimulant that US authorities refuse to approve because it can cause arrhythmia and possibly even sudden death. On top of that, says Nissen, these products are often ineffective for the conditions they claim to treat. And they could even prevent patients from checking out legitimate medications that actually work.

If they do seem to be making a difference, that may be cause for concern, too. “If a weight-loss supplement is working, its success could be due to a stimulant whose safety is unproven,” says Dr Arthur Agatston, a preventive cardiologist and member of the US Prevention advisory board. “Even if you lose weight, you may have unpleasant—even dangerous—cardiac side effects.”