"i have been on phentermine for a month and love it. the only side effects are dry mouth, lack of sleep and slight constipation. i did notice that after 2 weeks of being on it i did not have as much energy as i had in the first 2 weeks. i decided to take it monday through thursday and then start up monday again. that seems to work better for me. i am down 14 lbs in one month and i am so excited, 40lbs away from my goal.yeah."