Chemical Abstracts Service Registry Number: 122-09-8. (Hydrochloride form 1197-21-3)
Formal Names: Adipex-P, Duromine, Fastin, Ionamin, Obe-Nix 30, Umine
Informal Names: Robin's Eggs
Type: Stimulant (anorectic class). See page 15
Federal Schedule Listing: Schedule IV (DEA no. 1640)
USA Availability: Prescription
Pregnancy Category: C
Uses. Phentermine is primarily used on a short-term basis for weight reduction. The compound is related to amphetamine. Effects are similar to but weaker than those of dextroamphetamine. For example, phentermine can make users more physically energetic. A study found phentermine more effective than diethylpropion for promoting weight loss, a superiority attributed to phentermine's ability to retain therapeutic effectiveness longer before tolerance sets in. Standard medical practice is to stop taking the drug when tolerance develops, instead of increasing the dose.
In one study symptoms of depression improved among overweight people using phentermine. Researchers ascribe that improvement to the drug, but perhaps users simply felt good about shedding pounds. Some research indicates that the drug acts as a monoamine oxidase inhibitor (MAOI), which thereby associates phentermine with a number of antidepressants, but other research has challenged that finding.
Drawbacks. Phentermine may interfere with sleep, cause dry mouth, make bowel movements looser or harder, produce impotence, make people edgy and ill-tempered, or (in contrast) create euphoria. The compound is suspected of involvement with stroke, but reported cases have confounding factors. In one instance the patient had a history of headaches before taking phentermine and a family history of migraine and stroke. In another case the person was also taking phendimetrazine, had used birth control pills for 14 years, had smoked cigarettes for two decades, and had a personal history of migraines and a family history of high cholesterol and high blood pressure. Phentermine has also been linked to narrowing of abdominal arteries with a possibility of ruptured aneurysms there. Uncommon accounts exist of phentermine users developing primary pulmonary hypertension, a major and often fatal affliction involving blood circulation through the lungs. The drug is not recommended for persons with heart ailment, serious hardening of the arteries, high blood pressure, glaucoma, or an overactive thyroid gland. The drug may impair ability to operate tools and machinery, such as automobiles.
Someone taking phentermine came down with a psychosis that cleared up after stopping the drug. Initially the affliction was blamed on the drug, but the person later developed paranoid schizophrenia, a development suggesting that the drug promoted but did not cause the initial psychosis. The incident did not demonstrate that phentermine will cause psychosis in healthy people. With someone else, symptoms mimicking schizophrenia appeared when dosage of phentermine increased and stopped after ingestion of phentermine stopped. In another case a user began seeing people appear and vanish, heard things no one else could perceive, and started experiencing paranoia—afflictions attributed to the drug. Such reports became numerous enough that practitioners were advised to limit the drug's use to only a few weeks. Adverse psychological reactions are a known hazard of overdose. Physicians have publicly cautioned against exceeding recommended dosage and against prescribing to persons with personal or family histories of mental illness.
Abuse factors. Research is uncommon on phentermine's specific tolerance, dependence, withdrawal, and addiction potentials, but such factors are probably similar to those of stimulants in general. Animal and human experiments suggest that phentermine may help cocaine addicts decrease their use of the latter drug.
Drug interactions. Because of phentermine's possible MAOI properties it should normally be avoided if a patient is taking some other MAOI, and it may have untoward effect if alcohol beverages are consumed.
For years "fen-phen" was a widely prescribed weight reduction combination of phentermine and fenfluramine. In 1997 controversy arose about whether the combination caused serious and sometimes fatal heart disease; for details see this book's entry about fenfluramine. Heart disease has been reported following use of phentermine with other drugs as well and, more rarely, without taking any other drugs. In contrast, one practitioner who treated hundreds of patients with phentermine found no evidence of cardiac disease caused by the drug used alone or in combination with the antide-pressant fluoxetine (Prozac). That latter "phen-pro" combination has been reported as causing adverse reaction similar to amphetamine overdose, but such reports are uncommon.
Cancer. Not enough scientific information to report.
Pregnancy. Researchers seeking evidence of human birth defects report that standard medical usage in the first trimester found none attributable to the drug.
Additional information. Adipex-P and Fastin are the slightly less potent hydrochloride form of the substance (30 mg of phentermine hydrochloride roughly equals 24 mg of phentermine). The potential for causing cancer or birth defects is unestablished. This form may enter human milk if nursing mothers take the drug.
Additional scientific information may be found in:
Brauer, L.H., et al. "Evaluation of Phentermine and Fenfluramine, Alone and in Combination, in Normal, Healthy Volunteers." Neuropsychopharmacology 14 (1996): 233-41.
Devlin, M.J., et al. "Open Treatment of Overweight Binge Eaters with Phentermine and Fluoxetine as an Adjunct to Cognitive-Behavioral Therapy." International Journal of Eating Disorders 28 (2000): 325-32.
Douglas, A. "Plasma Phentermine Levels, Weight Loss and Side-Effects." International Journal of Obesity 7 (1983): 591-95.
Griffen, L., and M. Anchors. "The 'Phen-Pro' Diet Drug Combination Is Not Associated with Valvular Heart Disease." Archives of Internal Medicine 158 (1998): 1278-79.
Hoffman, B.F. "Diet Pill Psychosis: Follow-up after 6 Years." Canadian Medical Association Journal 129 (1983): 1077-78.
Jones, K.L., et al. "Pregnancy Outcomes after First Trimester Exposure to Phentermine/ Fenfluramine." Teratology 65 (2002): 125-30.
Kokkinos, J., and S.R. Levine. "Possible Association of Ischemic Stroke with Phentermine." Stroke 24 (1993): 310-13.
Langlois, K.J., et al. "Double-Blind Clinical Evaluation of the Safety and Efficacy of Phentermine Hydrochloride (Fastin) in the Treatment of Exogenous Obesity." Current Therapeutic Research: Clinical and Experimental 16 (1974): 289-96.
Was this article helpful?
Are you looking to lose weight or even just tone up? What is stopping you from having the body you want and help you feel great at the same time? I created Weight Loss All-Star for all those wanting to lose weight, and keep the weight off. I know how hard it is to do diets and stick with them, and get the motivation to get up and exercise.