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FAQ: Currently prescribed obesity medications.

Last update January 14, 2001. If you have a question about current obesity medications, please take a look at this list of questions.

Table of Contents

Peripherally acting drugs.

All of the medications listed below, with the exception of Meridia (sibutramine), are central nervous system stimulants. No drugs that act on serotonergic pathways are currently approved for weight loss, although a variety of medications are prescribed "off-label" with or without one of the drugs listed below. Meridia is in a class by itself. It is an "SNRI", that is a serotonin and norepinephrine reuptake inhibitor.

Rationale for using stimulants for weight loss. Stimulants enhance the neurotransmission of catecholamines (norepinephrine and dopamine) leading to increased sympathetic activity and reduced appetite. All noradrenergic agents act by activating central beta and/or dopaminergic receptors in the hypothalamus, the hunger center of the brain. Stimulants which act on dopamine, like amphetamine, have high abuse potential, and are not used in the treatment of obesity. The drugs listed below act primarily by enhancing the release and/or inhibiting the reuptake of norepinephrine (noradrenaline), and have very low abuse potential when taken as directed.

Diethylpropion (Tenuate).

Diethylpropion is a stimulant used for weight loss. It is available in both immediate and controlled-release pills. Tenuate is a 25 mg pill which is generally taken before each meal. Tenuate dospan is a 75 mg controlled-release tablet which is taken once a day, usually in the morning. Diethylpropion is no longer under patent protection, and is manufactured and distributed by many pharmaceutical companies.

Phendimetrazine (Bontril)

Phendimetrazine is another stimulant prescribed for weight loss. Some physicians prescribe it in combination with phentermine to reduce drug tolerance. Phendimetrazine comes in a 35 mg tablet taken before meals. Like diethylpropion, phendimetrazine is no longer under patent, and is now manufactured by several companies. It is a schedule 3 medication. Most centrally acting obesity drugs are under schedule 4.

Phentermine (Adipex-P, Fastin, Ionamin).

Phentermine is the most commonly prescribed of the stimulant anorexiant medications. Phentermine hydrochloride has been available in the United States since the early 1970s and phentermine resin since 1959. Phentermine hydrochloride comes in both time release and immediate release formulations: a 37.5 mg immediate release tablet (Adipex-P), 15 and 30 mg time release capsules (Fastin), and an 8 mg immediate release pill (generic only). There are many, many generic manufacturers and distributors of phentermine HCl and also several lesser known brand names. Phentermine resin (Ionamin) comes in 15 and 30 mg capsules. It is not a "time release" medication per se, but phentermine is released more slowly from the resin and therefore many patients find they have fewer side effects when taking Ionamin. Phentermine resin is not available in a generic.

Obesity-news has covered recent studies on phentermine, but since it is an older drug, no new efficacy trials have been conducted. The one notable exception, are several trials on the combination of fenfluramine and phentermine in the early and mid 1990s. The most famous of those trials was the four-year study conducted by Michael Weintraub. In addition, recent studies on phentermine combined with other medications have been conducted, including one on phentermine and orlistat (Xenical) and phentermine and bupropion (Wellbutrin -- subscribers).

Sibutramine (Meridia®)

Sibutramine, which was approved as an anti-obesity drug in February 1998, is a serotonin and norepinephrine reuptake inhibitor (SNRI) that works on hunger centers in the brain. Unlike phentermine and fenfluramine which affect the release and the reuptake of dopamine, norepinephrine and serotonin, Meridia® primarily affects the reuptake of norepinephrine and serotonin. It does not release neurotransmitters from the synapse. Most patients who take Meridia can expect to lose 5-10 percent of their body weight taking this drug. Like with most obesity medications, the majority of patients will not become normal weight taking Meridia, even with additional exercise and a change in diet. However, the weight loss will improve the health of most patients, and reduce the risk of obesity related diseases. In 1998 Obesity-news ran a survey on Meridia, which found that most patients who previously took phen/fen did not respond well to sibutramine. The results are available on our Obesity-101 site.

Obesity-news has covered sibutramine extensively over the past few years, including a monograph in 1997 (subscribers) and in-depth coverage of the Knoll press conference in February 1998 (subscribers). In addition, Obesity-news has reported on many of the efficacy studies and research on sibutramine and metabolic rate.

Benzphetamine (Didrex)

Along with phendimetrazine, benzphetamine is a schedule 3 drug. It is dispensed in scored 50 mg tablets, and prescribed in 25 mg to 50 mg doses one to three times per day.

Mazindol (Sanorex)

Mazindol is another less frequently used anorectic medication, dispensed in 2 mg pills up to 3 times daily before meals.

  • Mazindol monograph. (no longer on-line)

Xenical. (orlistat)

Xenical is a fat blocking pill that absorbs up to a third of dietary fat. It is taken three times a day before meals. Xenical was supposed to be approved before Meridia, but some unexplained incidences of breast cancer showed up in the Xenical group during phase III clinical trials. All the women who had breast cancer developed it in the first six months of the trial, and an independent review panel determined that it was likely they already had the tumors when they entered the study. Xenical is not a systemic drug, and therefore it is unlikely that it caused these cancers.

The Food and Drug Administration agreed with Roche's independent review panel which concluded that the breast cancer incidences were a statistical glitch and approved Xenical for use on April 26, 1999.

Pill identification.

Obesity-news has several resources on the site to help you identify your weight loss medication. Pictures of Xenical can be found on the Obesity-news Xenical page, and a pictures of the 5 mg, 10 mg and 15 mg Meridia capsules can be on the Merida page. In addition, RXList has a pill identification search engine on thousands of prescription medications.


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