Phentermine (phenyl–tertiary-butylamine), sold under the brand name Ionamin among others, is a medication used together with diet and exercise to treat obesity. It is taken by mouth for up to a few weeks. After a few weeks the beneficial effects no longer occur. It is also available as the combination phentermine/topiramate.
Common side effects include a fast heart beat, high blood pressure, trouble sleeping, dizziness, and restlessness. Serious side effects may include pulmonary hypertension, valvular heart disease, and abuse. Use is not recommended during pregnancy or breastfeeding. Use is not recommended together with SSRIs or MAO inhibitors. It works as an appetite suppressant likely as a result of being a CNS stimulant. Chemically, phentermine is a substituted amphetamine.
Phentermine was approved for medical use in the United States in 1959. It is available as a generic medication. The wholesale cost of a month supply in the United States is about US$2.55. In 2017, it was the 210th most commonly prescribed medication in the United States, with more than two million prescriptions. Phentermine was withdrawn from the market in the United Kingdom in 2000 while the combination medication fen-phen, of which it was a part, was withdrawn from the market in 1997 due to side effects
Phentermine is used for a short period of time to promote weight loss, if exercise and calorie reduction are not sufficient, and in addition to exercise and calorie reduction.
Phentermine is approved for up to 12 weeks of use and most weight loss occurs in the first weeks. However, significant loss continues through the sixth month and has been shown to continue at a slower rate through the ninth month.
Phentermine use is contraindicated in those who:
- have a history of drug abuse.
- are allergic to sympathomimetic amine drugs.
- are taking a monoamine oxidase inhibitor (MAOI) or have taken one within the last 14 days.
- have cardiovascular disease, hyperthyroidism, or glaucoma.
- are pregnant, planning to become pregnant, or breast-feeding.
Rare cases of pulmonary hypertension and cardiac valvular disease have been reported. Tolerance usually occurs; however, risks of dependence and addiction are considered negligible. People taking phentermine may be impaired when driving or operating machinery. Consumption of alcohol with phentermine may produce adverse effects.
There is currently no evidence regarding whether or not phentermine is safe for women who are pregnant.
Other adverse effects include:
- Cardiovascular effects like palpitations, tachycardia, high blood pressure, precordial pain; rare cases of stroke, angina, myocardial infarction, cardiac failure and cardiac arrest have been reported.
- Central nervous system effects like overstimulation, restlessness, nervousness, insomnia, tremor, dizziness and headache; there are rare reports of euphoria followed by fatigue and depression, and very rarely, psychotic episodes and hallucinations.