Phentermine, sold under the brand name Adipex-P among others, is a medication used together with diet and exercise to treat obesity.

[3] Common side effects include a fast heart beat, high blood pressure, trouble sleeping, dizziness, and restlessness.

[3] Phentermine is an norepinephrine and dopamine releasing agent (NDRA) and produces stimulant, rewarding, and appetite suppressant effects.

[3] Phentermine is contraindicated for users who:[5][15] Tolerance usually occurs; however, risks of dependence and addiction are considered negligible.

[8][10] The drug robustly and dose-dependently elevates brain norepinephrine and dopamine levels in animals.

[8][9][10] Unlike many other amphetamines and MRAs, phentermine is completely inactive at the vesicular monoamine transporter 2 (VMAT2).

[10][27] Although phentermine induces the release of dopamine at sufficiently high concentrations in vitro and at sufficiently high doses in rodents and monkeys in vivo, it may result in only weak or negligible brain dopamine release in humans at typical clinical doses.

[9][10][27] This is in contrast to the serotonin releasing agents (SRAs) fenfluramine, norfenfluramine, and to a lesser extent chlorphentermine.

[9][27] However, another study found that phentermine was a weak human serotonin 5-HT2C receptor partial agonist (EC50Tooltip half-maximal effective concentration = 1,394 nM, Vmax = 66%).

[32][10][27] Phentermine has been found to be active as an agonist of the rat and human trace amine-associated receptor 1 (TAAR1).

[33][34][35][36] It appears to be a weak human TAAR1 partial agonist (EC50 = 5,470 nM and EmaxTooltip maximal efficacy = 68% in one study).

[6] In 1959, phentermine first received approval from the US Food and Drug Administration (FDA) as an appetite suppressant.

[43] Phentermine was marketed with fenfluramine or dexfenfluramine as a combination appetite suppressant and fat burning agent under the popular name fen-phen.

[44] In 1997, after 24 cases of heart valve disease in fen-phen users, fenfluramine and dexfenfluramine were voluntarily taken off the market at the request of the FDA.

[45] Studies later showed nearly 30% of people taking fenfluramine or dexfenfluramine for up to 24 months had abnormal valve findings.

[51][52][53] A number of derivatives of phentermine exist, including cericlamine, chlorphentermine, cloforex, clortermine, etolorex, mephentermine, 3,4-methylenedioxyphentermine (MDPH), 3,4-methylenedioxy-N-methylphentermine (MDMP or MDMPH), and pentorex, among others.

It is marketed under many brand names and formulations worldwide, including Acxion, Adipex, Adipex-P, Duromine, Elvenir, Fastin, Ionamin, Lomaira (phentermine hydrochloride), Panbesy, Qsymia (phentermine and topiramate), Razin, Redusa, Sentis, Suprenza, and Terfamex.