Medication and Weight Gain

It is thought that weight gain can occur with certain drugs, but the research into this is often conducted on small patient populations, is only short term and can be poorly controlled. Whilst some people may gain weight when starting on a certain class of drugs, others may not, and the weight that is gained may not necessarily be fat, but may be fluid or lean body mass. Some of the weight gained when starting certain medication such as anti-depressants can be due to improved mood and therefore eating habits, and can often be replacing weight the patient had lost before starting the medication.

The best strategy is to try and prevent or limit weight gain when starting on medication that is associated with weight gain. It is also important to let patients know that these drugs do not prevent them from losing weight.

The following are certain classes of drugs that are associated with weight gain:

Anti-psychotics:

• Increase appetite - alter sensitivity of central nervous system to leptin
• Increase prolactin and adrenal steroids
• Decrease insulin sensitivity and metabolic rate

Upto 50% of patients gain weight in the long term and often in the first 12 weeks, with underweight patients gaining the most weight. Improved mood, decreased activity and increased fluid intake may be responsible for weight gain. Treatment with Metformin has been shown to help stop weight gain and suppress appetite.

Steroids

• Alter protein and carbohydrate metabolism leading to insulin resistance.
• Cause water and sodium retention which may be responsible for weight gain.

Anti-depressants

• Can cause carbohydrate cravings, increased appetite and decrease in metabolic rate.
• Tricyclic anti-depressants cause the most gain through carbohydrate cravings and decrease in metabolic rate.

Beta Blockers

• 4-9% reduction in resting metabolic rate.
• 25% reduction in thermic response to food.
• Reduced exercise tolerance and earlier fatigue (5-19% reduction in energy expenditure)
• Reduced breakdown of fat and increase in insulin resistance.