First let me say that diet pills are almost always faux
speed, not even remotely like steroids. People use them in working out to get more "motivated" and to "work through the pain". If you are going to take them (which I don't recommend) I'd do a little more research on the active medical ingredients in your paticular happy pills. Don't take some guy's word for it at the gym just because he has bigger muscles than you.
I think your dream is telling you that deep down you are worried about the consequences of taking some weird drug you don't really know the effects of. Promise yourself that you will look before you leap.
Later ----------- CloudHelmut