Why Do Phentermine Diet Pills Give Me Mood Swings?

The diet pill phentermine is associated with a number of negative and dangerous side effects, but it is still sold as a commercial appetite suppressant. Doctors may prescribe this medication to treat obesity, and it was part of the widely used yet discontinued Phen-Fen combination, which also included fenfluramine. Consult your doctor immediately if you experience adverse effects such as mood swings while taking phentermine.

About Phentermine

Phentermine, sold under the brand names Adipex-P, Oby-Cap, T-Diet and Zantryl, is a stimulant drug that belongs to the anorectics class of medications and has effects similar to those of amphetamines. It is typically used as an appetite suppressant, which works by affecting your central nervous system. Phentermine helps to control your appetite by increasing the amounts of certain chemicals that signal to the part of your brain that controls appetite. You feel more satisfied more quickly and are not as likely to overeat.

Safety and Effectiveness

In a Feb. 1, 2009 article for ABC News Health, Howard Eisenson, M.D., executive director of the Duke Diet and Fitness Center, wrote that phentermine appears to be "moderately effective," in that most people who use it tend to lost three to five pounds more than if they did not use the medication. However, phentermine is intended to be used in combination with diet and exercise, and you should use phentermine only for a short time. The duration of use should be determined by your doctor, but is generally used for no longer than a few weeks, according to Drugs.com. Phentermine is associated with a number of serious side effects, including shortness of breath, irritability, confusion, thought problems, chest pain and ankle swelling, as well as less serious side effects like restlessness, hyperactivity, headaches, sleep problems, digestive complaints and decreased sex drive, according to Drugs.com.

Phentermine and Mood

Phentermine may cause mood swings, although this should be a short-lived side effect, according to Mark Davis, M.D. in his book, "The Millenium Diet." Because phentermine is a stimulant drug, it alters the release of certain brain chemicals like adrenaline, which control your appetite. However, this can alter your heart rate and cause insomnia, mood swings and related symptoms of anxiety and irritability, according to Professor Hamid Ghodse, former president of the UN's International Narcotics Control Board and chairman of addiction psychiatry at St. George's Hospital, London, in a May 29, 2007 interview with the "Daily Mail."


Phentermine can interact with a number of medications and cause serious side effects. You should not use phentermine if you are pregnant or nursing or have a history of depression or heart disease. Do not use phentermine if you have taken an MAOI, a type of drug typically used to treat depression, in the past 14 days. Avoid other stimulants, such as caffeine, while using phentermine. Consult your doctor immediately if you experience any negative side effects while using phentermine.

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