How To Take Phentermine For Best Results. The best way to take Phentermine to lose weight depends on which form you have. Tablet: This tablet may be taken either before breakfast or one to two hours after eating breakfast. As such, phentermine should be used not as the primary way to lose weight but as a supplement to a healthy exercise and diet. According to Mayo Clinic , side effects of the fast weight-loss drug may include: Although phentermine is one of the most commonly prescribed weight-loss medications, it isn't a good option if you have heart disease, high blood pressure, an overactive thyroid gland or glaucoma. It also isn't for women who are pregnant, may become pregnant or are breast-feeding. Best Answer: Remember how much you ate while on the phentermine and try to keep to that once you go off it. I'm about to go off mine after 3 months and I'm a little worried too about that. I'm 15 and I used to abuse phentermine. My mom was taking it, and I found a medical book and I looked it up and saw that you could get high from it. You should not use phentermine if you have glaucoma, overactive thyroid, severe heart problems, uncontrolled high blood pressure, advanced coronary artery disease, extreme agitation, or a history of drug abuse. Phentermine should not be used by patients with high blood pressure, cardiovascular disease, glaucoma, hyperthyroidism, substance abuse issues, or by women who are pregnant or might become pregnant or breastfeeding. Certain drugs are more susceptible to abuse than others because of how they affect the body and the mind. Phentermine addiction, for instance, is a possibility for anyone taking this medication to treat obesity. Best Answer: I don't know why you would ever take 2 and I don't know why your doctor would say that. It can be a dangerous drug (you have to watch your heartrate and any other worrying signs). This way the online seller of Phentermine has no obligation to write small print stating that it’s not as advertised. Although the product does contain the proper ingredients, it will have no effect on your fat loss.