There have been dangerous weight loss supps in the past like that Phen-Phen stuff and it's possible that newer weight loss products will come out that will cause harm.
Right now most are just useless and contain caffiene and vitamins which give energy but do not increase fat metabolism enough to notice. Especially if you don't diet.
The one that worked was the ephedrine/caffine stack but last I heard it was banned by the FDA.
It's not clear if the reported harmful effects were from proper use or overdose?
I've known several people who used those products for years and swore by them. I used them once and had unusually good results while on a cutting phase. But one day while using "Ripped Fuel" I went online and read about reports of strokes/heart attacks and was never able to use it again because I would work myself into a panic attack. That was the beginning and end of my experience with stimulants (except coffee). Never again.