I took Phentermine for months. I must say that I lost about 15lbs with it but although it did not make my heart race or make me shaky it made me stay awake, I wasn't hyper and was tired but couldn't sleep. I realized that if I missed a day on it I would crash really bad and I would sleep the day and night away. So I started to take it so that I wouldn't crash BUT it stopped helping me in the weight loss department and I just became an insomniac! I became addicted to it because I feared the consequences if I got off of it. When I finally weened myself off of it I had horrible sleeping patterns and actually became very irritable, I had to take anti depressants and sleeping pills just to get me back to normal and with all of that going on I ended up gaining all of my weight back..honestly I would not recommend this to anyone! I have never been able to keep up with pills in my life and have never been addicted to anything other than cigarettes but this was a horrible experience for me all around. The whole process was about 2 years long and now I am fat but back to normal at least.