"hi , i&#039;m 40. 5-11 290 male when starting phentermine 37.5 mg. i figured i better post and help someone maybe not go through what i went through the 1st three days . take on full stomach !!!!! i took this med on semi empty stomach the first 2 days and i thought i was going to come out of my skin it was horrible horrible feeling like i never felt !!!  i stopped my dose after day 2 and didn&#039;t wear off for another full day and slept 1hr in those 3 days !!!!! so day 4 i tried on a full stomach and no probs just the normal bad cotton mouth . i work swing shifts so i learned if your going to take this med take it as if it&#039;s not going to wear off for 16hrs. if you do this you&#039;ll be able to sleep if not good luck lol. lost 18 pounds this month"