Phentermine should be prescribed as part of a weight loss plan that also includes exercise, modifying behavior and reducing calories. Phentermine is usually taken for 12 weeks or less. Weight loss effects depend on the dose of phentermine taken, as well as diet, exercise and other factors. How long does phentermine stay in your system? Phentermine stays in your system for approximately 4 days after you take it. It takes about 20 hours for half of the drug to leave your system. Many things affect how long it takes a drug to leave your system. These include your age, diet, how well your kidneys and liver are working and other factors. How to take phentermine for the best results? Take phentermine as directed by your doctor. It is usually taken first thing in the morning, before breakfast. It may also be taken 1 to 2 hours after eating breakfast. Phentermine is not usually taken at night because it can cause insomnia. http://avionlinestore.com/