Phentermine is a controlled substance, meaning it may only be purchased with a prescription from a doctor, according to EverydayHealth. Generally, phentermine is only prescribed to patients who have a body mass index that is 30 or greater.
Phentermine is habit forming, and when it is taken for more than a few weeks, it's possible to become dependent on the drug, explains EverydayHealth. Phentermine should never be taken with any other types of weight loss pills or supplements. People who take phentermine should exercise and cut back on calories as well. Those with certain medical conditions such as hardening of the arteries, heart disease, overactive thyroid and glaucoma should not take phentermine. Individuals with a history of drug abuse are also advised not to take the drug.
Patients should stop taking phentermine and contact their doctors if they experience difficulty breathing, chest pain, feeling faint or swelling in the extremities, according to EverydayHealth. Pregnant women should never take phentermine, as it can harm the fetus. Breastfeeding while taking phentermine is not recommended. Drinking alcohol should also be avoided, as it can counteract the effects of phentermine because it is a depressant and phentermine is a stimulant. Phentermine should only be taken for a short period of time.