cyanide

Gold is known as a noble metal because of its lack of chemical reactivity. But if you treat it right, you can get it to do some cool things. You can chew on it, make some lousy drugs, screw up the environment mining it, and (maybe) even make a super-pricey burger. Really.
Instead of getting a flu shot, a Columbia University professor who believes in natural remedies chose a "tincture of elderberry." Her effort was rewarded with cyanide poisoning.
We sometimes think that if you give people true, scientific information they will listen. But then that theory is blown away by a reality check, such as with the case of an Australian man who continued to take supplements derived from apricot kernels – that doctors told him was giving him chronic cyanide poisoning.
Apricot seeds are all over the internet - marketed as cancer fighters. But the seeds contain a chemical compound that, when ingested in high quantities (and by high we mean several seeds), can cause cyanide poisoning.