What's the worst that could happen from taking some metabolism pills?

Metabolism pills: BEWARE They are supplements that have no controls on what is in them. Some have died from arsenic in them. I would call that the worst. Some have gotten mercury poisoning. Not as bad as dying but pretty bad as you go crazy like a Mad Hatter. Some have viagra in them could be good or bad. Some have testosterone n them and you could become very strong and have a beard Bad or not?