1. Because they are virtually unregulated

2. The regulation lacks teeth

3. People are too eager to rush for a silver bullet than take the slow but sure road to better health.

· According to a new Harvard study today, as many as 11 supplements on the market contain the potentially dangerous ingredient. They were all available at popular retail stores and online, and are advertised as "all-natural."

· A similar study, carried out by the FDA in 2013, found BMPEA in 9 of 21 tested supplements, but no regulatory action was taken. No public warning was issued.

· Just this week, Human breast milk sold were found to be tainted with cow’s milk.

· In 2013, Researchers identified 27 supplements available for purchase online that were among 274 recalled during 2009-2012. Among sports enhancement or bodybuilding supplements, 85% of those purchased by the researchers remained adulterated with dangerous compounds, including anabolic steroids

· Any more recently, in Feb 2015, GNC, Target, Wal-Mart, Walgreens were accused of selling adulterated ‘herbals’. The investigators tested 24 products claiming to be seven different types of herb — Echinacea, garlic, gingko biloba, ginseng, saw palmetto, St. John’s wort and valerian root. All but five of the products contained DNA that was either unrecognizable or from a plant other than what the product claimed to be.

Still not Convinced?

Here are more from Medscape

So, What should a consumer do?

From FDA: consumers should heed these potential warning signs of tainted products marketed as dietary supplements.

• Products claiming to be alternatives to FDA-approved drugs or to have effects similar to prescription drugs.
• Products claiming to be a legal alternative to anabolic steroids.
• Products that are marketed primarily in a foreign language or those that are marketed through mass e-mails.
• Products that provide warnings about testing positive in performance enhancement drug tests.

Generally, if you are using or considering using any product marketed as a dietary supplement, FDA suggests that you

• check with your health care professional or a registered dietician on any nutrients you may need in addition to your regular diet
• ask yourself: Does it sound too good to be true?
• Be cautious if the claims for the product seem exaggerated or unrealistic
• Watch out for extreme claims—for example, "quick and effective," "cure-all;" "can treat or cure diseases; or "totally safe"
• Be skeptical about anecdotal information from personal “testimonials” about incredible benefits or results obtained from using a product
• ask your health care professional for help distinguishing between reliable and questionable information