In the news article from the site dopingautoriteit.nl you can read about the nor-DMAA containing supplement Unstoppable (Dedicated Nutrition). Nor-DMAA (DMBA) can be found in many supplements and a also the similar substance DMAA is being used by different manufacturers.

Amphetamine derivatives

Adding amphetamine analogues and similar substances are very common in weight-loss supplements. Sibutramine is another frequently used substance. The question then is whether the manufacturer or supplier has deliberately added this. It also can be an accidental contamination due to an error in the manufacturing process. It certainly does work for specific purposes, such as fat burning or as a stimulant. Because of this it is tempting for manufacturers to put it in fat-burning and energy boosting supplements.

Heavy metals

Unfortunately, these are not the only possible contaminants in your supplements. Heavy metals such as mercury, arsenic and lead are also frequently found. The property to operate as an energy booster is missing with these substances. For weight loss it may work, but the drawback is that you can get seriously ill. Lead and arsenic are so poisonous that there is no acceptable daily intake. In high doses, it even can be fatal, in lower doses, there is always a risk of physical damage.

Hormones

Other possible contaminents are prohormones, hormones, anti-estrogens, viagra, clenbuterol, antidepressants and anabolic steroids. Sometimes there are no impurities, but at the same time the substance which is supposed to be in it is nowhere to be found. On ergo-log.com you can read all the articles on possible contaminations like heavy metals in whey. OxyElite has created a long list of liver transplants this way.

Test Organizations

The organization Consumerlab.com conducts regular studies on contaminants in supplements. But they also test whether there is in it what is supposed to be in it, and in what quantity. This they also have done for whey, but to see the results you have to subscribe to their site. Also, it is mainly USA brands being tested.

As you can see in the link below, sometimes supplements just contain something else.
GNC, Target, Wal-Mart, Walgreens accused of selling adult rated 'herbals'