obesity
"Read some reviews here, can relate to someone that said they had palpitations and feeling of " closing of the throat". You are either taking too much or you might have already a tendency to anxiety and as a stimulant, this medication will increase symptoms of anxiety. 
What can also help in case of the negative reactions, besides lowering the dosage, is DEFINITELY take the pill with at least an 8 oz glass of water to help dilute some of the strength of this diet aid. Taking it with a full glass or skim, soy or almond milk will be also soothing of negative symptoms. "