Weight loss drugs: Fluoxetine (Prozac)

Fluoxetine, better known by its brand name Prozac, is one of the world's most recognized antidepressants. Yet few people know that fluoxetine is also a weight loss-inducing drug. Initially, the reports of weight loss effects of fluoxetine were explained by its antidepressant action. Indeed, some people respond to depression by overeating; hence, successful treatment of depression may reduce overeating thereby improving weight control. However, most other antidepressant didn't show similar weight loss benefits. Furthermore, fluoxetine seemed to induce weight loss whether patients were depressed or not. As a result, some physicians started using fluoxetine off-label to treat obesity, which in turn, prompted further studies.

Fluoxetine (Proazac) belongs to the class of drugs called selective serotonin reuptake inhibitors (SSRI). SSRI work by blocking the recycling of the neurotransmitter serotonin, which causes serotonin level in the brain to increase. It is not quite clear how fluoxetine promotes weight loss. Many experts believe that fluoxetine acts mainly as appetite suppressant because serotonin is know to have a role in appetite regulation. However, some studies indicate that fluoxetine increases metabolic rate suggesting a different a different mechanism for its weight loss effect. Yet other studies failed to show any changes in metabolic rate in patients taking fluoxetine.

Whatever its mechanism of action, in studies that used a dose of 60 mg once daily, fluoxetine-treated patients consistently had greater weight loss than placebo-treated patients. Fluoxetine may be of particular benefit in obese patients with diabetes or prediabetes. Dr. Wise, from Lilly Research Laboratories, Indianapolis, analyzed several fluoxetine studies and concluded the following:

Longer term studies have shown maximum mean weight loss to occur at 12-20 wk of therapy. Studies have consistently shown improvements in indices of glycemic control as well as weight loss in obese diabetic patients. Safety analysis has been performed on data from 3491 obese patients in controlled clinical trials of up to 52 wk duration. Adverse events with an incidence of greater than 5%, which were reported significantly more frequently by fluoxetine-treated patients, were headache, asthenia, nausea, diarrhea, somnolence, insomnia, nervousness, sweating, and tremor. Fluoxetine is effective, well tolerated, and safe in the treatment of obesity and obese diabetics.

Despite the above evidence of effectiveness, fluoxetine has not been approved for weight loss by the FDA as of the time of this writing. There are some good reasons for that. Weight loss on fluoxetine, while proven, tends to be relatively small: a few kilograms (a kilogram is 2.2 pounds) on average, even though results vary markedly and some people achieve significantly greater weigh loss. At the doses shown effective for weight loss, fluoxetine causes frequent side effects, such as headache, asthenia, nausea, diarrhea, somnolence, insomnia, nervousness, sweating, and tremor. Finally, fluoxetine is a powerful mood altering drug, whose long-term use, especially in non-depressed subjects, is under-researched and may have negative consequences.

On the whole, the benefits of using fluoxetine for weight loss may outweigh the risk in a subset of carefully selected patients (e.g. depressed obese individuals with pre-diabetes). However, this should be determined by a physician closely familiar with the patient's medical history.

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