how many times a day can you take phentermine

Once a day and that perferably in the morning or you wont be sleeping at night. I've been taking phentermine under a doctors care for 8 months and it really helps but seems after several months my body adjusts to it so I got off for a couple of months and then got back on and back to losing weight again. I have lost a total of 35 pounds. I work out with it because I don't want saggy skin and if you lose slowly and exercise it helps keep that from happening.