If you've mastered your weight loss (and I'm assuming this means you're able to eat properly and control your cravings, along with exercising and drinking lots of water), then you can stop taking the Phentermine whenever you want. It actually stops working for you after about 3 months because your body gets used to it and it loses it's effectiveness. Sometimes people stop taking it temporarily, then start back after a few more months. Those are usually people who have a LOT of weight to lose and the pills have lost their effectiveness.
If you're able to lose the weight on your own now, that would be the healthiest choice...and good for you!! :-)
I have not been on the pills for almost 6 months. But I am still on the b12/b6 shots. I will stay on them for the rest of my life because I do like the extra energy that they do give me. Which I take every two weeks. I think I will be taking those the rest of my life.
I did get weened off of them over a 3 month period. I heard that going off of them cold turkey can be hard and the body does crash. Talk to your dr. and ask what he suggest.