Clenbutrol doesn't contain anything particularly dangerous, but it also doesn't contain anything that's particularly good for a weight loss supplement.
Vitamin b3 isn't bad for you, it just doesn't actually do very much when it comes to weight loss or fat burning. There was one mouse study that suggested it could, but that's not reason to include it in a supplement for humans.
Hydrocycitric acid did have it's moment in the sun, it actually looked like it was going to be really interesting when it was tested on animals, the problem was that it didn't translate to humans. It has been tested multiple times in human trials, but showed absolutely no difference when compared against a placebo group. There was a time when supplements could get away with this sort of claim, but now we're long passed that point.
Bitter Orange is the next ingredient to get hammered in our clenbutrol review, it's sadly the second best ingredient in this supplement and it's still terrible. It does nothing aside from being an incredibly mild stimulant. And we do mean very mild. Any claims that this product will help you shred body fat, or build lean muscle mass are quite simply false.
Guarana Extract, otherwise known as the only ingredient in our clenbutrol review that isn't awful. Although it could be, it's simply that the jury is out on that. The animal studies look good and the initial studies on humans (not double blind) don't look too bad. But, a lot of this seems to be down to the fact that it has some small amount of caffeine in it, again it's not going to help you lose much if any body fat.
So in short, Clenbutrol doesn't contain anything that can actually help you maintain lean muscle whilst dieting as it claims, even something as cheap as vitamin d would be better than anything in this supplement. As for direct fat loss there's also basically nothing in here that can help suppresses appetite, or speed up thermogenesis.