Weight loss: Fat drugs

Prescription drugs like Xenical and Reductil have made headlines; bringing hope to people suffering from obesity. But do these so-called ‘fat drugs’ really offer a solution? Dr Wynnie Chan investigates

When treating obesity, health professionals usually recommend dietary management and regular physical activity, among other lifestyle changes. In severe cases, however, new anti-obesity drugs, such as Xenical (the generic name is Orlistat) and Reductil (generically known as Sibutramine) may be prescribed.

Xenical, manufactured by Roche, works by inhibiting the enzyme that breaks down fat in the body, and therefore blocks the digestion and absorption of around 30 per cent of consumed fat. This undigested fat remains in the gut and then is excreted.

Reductil, manufactured by Knoll Ltd, works at the other end of the body as an appetite suppressant. It blocks the action of the naturally occurring chemicals serotonin and noradrenaline that send hunger signals to the brain. The drug helps patients to feel full, and causes them to eat less; they consequently lose weight.

Doctors determine whether someone is overweight or obese by measuring Body Mass Index (BMI), a calculation determined by dividing your weight in kilograms by your height in meters squared:

If your BMI is between 30 and 40 or higher, you are clinically obese. The following figures indicate what BMI means for your weight and health:

BMI at or below:
18.5................Underweight
18.5-24.9.........Healthy weight
25-29.9...........Overweight
30-34.9...........Moderately obese
35-39.9...........Severely obese
At or above 40..Morbidly obese

Both Xenical and Reductil are prescription only and meant for moderately obese patients with a BMI of 30 or more, or for overweight patients with a BMI of 27 or 28. The drugs may also be prescribed when the BMI is higher and the patient is at risk from factors like high blood pressure, diabetes, or heart disease.

Xenical will only be prescribed if the patient has first lost at least 2.5kg (5.5 lbs) over a four-week period of dieting alone. This is to ensure that the patient is sufficiently motivated and inclined to make the necessary effort to lose the weight required. Prior weight loss is not required for Reductil. Treatment with Xenical will be discontinued if patients haven’t been able to lose at least 5 per cent of their body weight after 12 weeks of taking the drug. This percentage is regarded as a good indicator that the drug is not working so is not the right form of weight loss therapy for this patient. With Reductil, treatment is also discontinued in patients who regain 3kg (6.6 lbs) or more while still on the drug, after previously achieving weight loss.