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Qnexa for Weight Loss; Side Effects

Drug Case

Qnexa is a new medication that will go for FDA approval in 2010 and is a treatment for obesity.  It consists of phentermine and topiramate and has shown excellent results in studies to date.  Concerns, however, remain about its safety and long run effectiveness.

Medications to help people lose weight have had a rocky history. It is very hard to get people who are obese or significantly overweight to lose weight.  The problem arises from the complex nature of obesity, which is likely caused by a variety of causes including lifestyle and genetics.  Most treatments on the market today focus on just one molecular pathway.

This has resulted in decent efficacy.  Many treatments achieve a 5-10% reduction in weight.  This does not always result in the looked for cosmetic differences, however.  Qnexa, which combines two treatments, shows impressive results.

In one study over 24 weeks, those on Qnexa lost about 25 pounds of weight compared to about 11 pounds in those taking phentermine alone or about 14 pounds in those taking topiramate alone.  That’s pretty impressive.

Isn’t Phentermine part of “phen-fen,” which was removed from the market?

Phentermine and fenfluramine was one of the most effective treatments for weight loss.  Despite its efficacy, however, the combo (given the moniker “phen-fen”) was removed from the market due to concerns about very increased risk of heart disease in those taking it.

So is Phentermine safe for use in Qnexa?

Likely.  Most of the problem from phen-fen seems to have been from the fenfluramine component.  It is likely that its effects on the chemical messenger serotonin somehow specifically targeted certain receptors in the heart.  And this caused the problems.

Phentermine is widely used today and has more than 50 years of use in general with little cardiac problems.  It does have amphetamine like behavior, but may have less of a dopaminergic effect, which explains why people don’t tend to develop dependency on it.

Topiramate is the other component of Qnexa.  It is an anti-epilepsy drug that has a variety of chemical actions that affect the brain’s activity.  It also has significant weight-loss effects of its own.

Side effects from Qnexa:

Qnexa has the type of side effects you would expect from a diet pill.  Dry mouth, insomnia, differences in taste were common.

Other common side effects from Qnexa include a sensation of prickling in the skin and constipation.  The combination treatment seems to have less cognitive side effects and lower discontinuation rates than topiramate alone.  The phentermine component may raise blood pressure or increase heart rate.

Related Article:

  1. Obesity Drugs 2010, Which is the Best?


What is the Role of Drug Therapy in Treating Obesity?
Topiramate in the prevention and treatment of migraine: efficacy, safety and patient preference
Phentermine cardiovascular safety

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This post was written by on Friday, April 16, 2010. This author has written 223 posts on this blog and has 6309548 total posts views.

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  1. It will be interesting to see what effect this drug will have on the liver

  2. i want to know if you can take this medication.if you have high blood pressure.cause i take lisinapril 40mg.

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