I use Stimerex and Black Mamba on a regular basis, but not both at the same time. Stimerex does better with keeping me awake and alert, as far as fat burning...Its limited for me. I have to go off it for a while to gain the effects back. But mostly it just keeps me alert and untired. I train twice a day, so it helps to get me into the gym in the afternoon, and gets me going in the AM when I am feeling draggy. As far burning fat, if you are pretty lean already from your diet, it will help, but if you're carrying a lot of extra fat, it will take a while, and thats if you have started a structured diet plan. I would opt for something else that is a little more effective in that area.