Study finds anti-obesity drug reduces brain’s response to appetizing foods

Sibutramine (usually in the form of the hydrochloride monohydrate salt) is an oral anorexiant. Until recently it was marketed and prescribed as an adjunct in the treatment of exogenous obesity along with diet and exercise. It has been associated with increased cardiovascular events and strokes and has been withdrawn from the market in the US, EU, AU etc. 

Sibutramine is a centrally-acting serotonin-norepinephrine reuptake inhibitor structurally related to amphetamines, although its mechanism of action is distinct.

Now, researchers lead by Prof. Paul Fletcher at the University of Cambridge discovered that the anti-obesity drug sibutramine reduced brain responses in two regions of the brain, the hypothalamus and the amygdala, both of which are known to be important in appetite control and eating behavior.

Using functional magnetic resonance imaging (fMRI), the researchers measured brain activity while obese volunteers viewed pictures of appetising high-calorie foods - like chocolate cake - or pictures of low-calorie foods - like broccoli. The brain scanning was carried out both after two weeks of treatment with the anti-obesity drug, sibutramine (see structure above), and two weeks of placebo treatment. 

On placebo, it was shown that simply seeing pictures of appetising foods caused greater activation of many regions of the brain that are known to be important for reward processing. On sibutramine, however, they found that the anti-obesity drug reduced brain responses to the appetising foods in two regions of the volunteers' brain - the hypothalamus and the amygdala. These two regions are known to be important in appetite control and eating behaviour. Additionally, people who had the greatest reduction of brain activation following drug treatment tended to eat less and to lose more weight.

I quote....

"The most exciting aspect of these results is that they help us to see that brain and behaviour are fundamental to understanding and treating obesity. Simply because obesity involves major changes in body weight and body composition, it is easy to imagine that it is entirely 'a body problem'. These results remind us that the major cause of obesity in the West is over-eating, and this behaviour is regulated by reward and satiety processing circuits in the brain." 

Ref : Paul C. Fletcher et. al., The Journal of Neuroscience, October 27, 2010