A Philadelphia doctor has just completed a large study showing there is a drug that is not only excellent at preventing headaches, but it has a great side effect -- It makes people lose weight.

Medical reporter Cherie Bank talked exclusively with the lead investigator of the study and one of his most impressive patients.

Catherine Skinner went from a size 20 all the way down to a size 2 as a side effect of the medicine she's taking to get rid of her chronic migraine headaches.

"I had a migraine every single day and it didn't just involve the excruciating throbbing pain over one eye. It also involved severe nausea, vomiting, sensitivity to light and sensitivity to sound," Skinner said.

Headaches like that are unbearable and debilitating. Medicines to stop the pain stopped working, Skinner said.

Many of the medications people take to prevent their headaches cause people to gain weight, sometimes a lot of weight. And Skinner has taken them all -- beta-blockers, the calcium channel blockers, the anti-seizure medications and the SSRIs.

Skinner gained 90 pounds over the years, even though she didn't eat much.

So, Dr. Stephen Silberstein, of the headache center at Thomas Jefferson University Hospital, put Skinner on a drug he has just studied extensively.

Topiramate, or topamax, is an anti-seizure drug.

"This is the first of three trials that clearly demonstrates that Topiramate is spectacularly effective for the treatment of migraine," Silberstein said.

But Silberstein is also amazed that the same drug can help people lose weight, not gain it.

"Of the patients who took as little as 100 milligrams of Topirimate a day, had greater than 50 percent reduction of their migraine frequency. Even more amazing to me is the fact, on average, is those patients on average lost 3.8 percent of their body weight," Silberstein said.

But Topiramate can cause some side effects including troubled thinking, so doctors recommend starting with a low dose and building up slowly.

Some people on the drug get pins and needles, in which case you're told to take potassium or eat a banana. Finally, many people experience weight loss -- which a lot of people don't mind a bit.

Since starting Topamax, Skinner has very few minor headaches and she has lost 95 pounds.

"I absolutely have my life back," Skinner said.