Weight loss surgery can change the way medicines work

About a third of Australians are obese and some require surgery to help with weight loss. However the surgery can change the way medicines work. In Australian Prescriber, weight loss experts Dr. Teresa Girolamo and Rosemary Allin from Adelaide discuss how the doses of some medicines may need to be changed after bariatric (weight loss) surgery.

In Australia there are around 100,000 weight loss surgeries done each year. Some operations make the stomach smaller so you eat less, and others reduce the absorption of food.

"Like food, your body won't absorb medicines as well after surgery," says Dr. Girolamo. "If you are taking mood stabilizers or antidepressants, you may need to take more to have the same effect."

"After surgery, you may not be able to absorb slow-release medicines as well. You may need to crush some tablets or change them into a liquid form to help with absorption. It is also important to avoid medicines that affect the stomach lining like ibuprofen and aspirin," she says.

"After weight loss surgery, alcohol will be absorbed more quickly and cleared from the body more slowly. This could affect driving," says Dr. Girolamo.

"Birth control pills may not be reliable due to reduced absorption so you should consider other birth control methods.

"Also, you will need to take vitamin and mineral supplements for the rest of your life."

On a positive note, Dr. Girolamo says you may need less medicine for blood pressure, diabetes, pain or depression as you lose weight.

"A lot changes after weight loss surgery. Your doctor, pharmacist and dietitian can help you adjust to the changes," she says.