How dangerous is taking weight loss pills?

I'm desperate trying to lose weight.

I eat healthily

I exercise regularly and for one hour and a half - 2 hours at a time at the gym 3 days a week

I have an active job

I am fine medically

And here's the clincher.

I used to eat under 1,500 kcal's a day, and the doctor told me I'm just one of those people who has a slow metabolism and doesn't need much food per day.

I'm now eating under 1,000.

AND I'M STILL NOT LOSING WEIGHT.

I'm really started to despair and I'm turning to weight loss pills instead. I found one called "Firestorm" link

If I took this, how bad would it be? It says everything amazing but nothing bad...
How dangerous is taking weight loss pills?
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