BOSTON (CBS) – Prescription medications are meant to make us feel better, but many have a side effect that isn’t that well known.

They can cause weight gain.

Belinda Marsh works out faithfully, but she still gained 30 pounds over a short period of time. Her weight started to climb when she was prescribed insulin for Type II diabetes.

It turns out many common drugs can cause weight gain, including mood stabilizers, anti-inflammatories, and some high blood pressure medications.

Pharmacist Karen Falk says this consequence often takes patients by surprise.

“I think some people don’t ask. Some people assume everything is going to be alright with medication.”

The reasons why some drugs might cause weight gain aren’t always clear.

Some increase appetite or food cravings. Others might slow the body’s metabolism.

A compounding problem is that more exercise doesn’t always help with this type of weight gain.

Dr. Louis Amore added, “It tends to be demoralizing when people try and they keep bouncing back and they can’t understand why they’re not making progress.”

The first thing to do if the pounds creep up is ask if you can be switched to another drug, advised Dr. Arrone.

If that’s not an option today, it might be in the future.

Dr. Arrone said many alternatives to weight-gaining drugs are in the pipeline.

“The fastest growing area of medication development is the development of drugs in a given area that don’t cause weight gain, and that’s very very good news.”