Hi, I can not drink caffeine while on
phentermine. It just makes me more anxious (like I've had 20 cups of coffee). If I must have a cup, I drink it as the phen starts to wear off, but not much....like 4 oz.
The phenetermine will make you jittery, cause sleeplessness etc., especially during the 1st 2 weeks of use. I think the energy drinks are not so good, either, and the diet red bull just tastes awful. You shouldn't need it with the phen.