I have taken phentermine and phendimetrazine as an appetite suppressant and neither of them worked for me. I've been going to a weight loss doctor and he has now prescribed diethylpropion 75 mg controlled release. I have taken it for two days and still have not noticed a difference. I was wondering how quickly it was supposed to work. I know the 25 mg pills are supposed to work immediately. Also, if anyone is taking the 75 mg, what time of day do you take it and is it on an empty stomach? I've lost 13 lbs so far on just dieting, but if the appetite suppressant would work, I'm sure I could lose more. Thanks for your help.