I don't know about a study to scientifically prove it.
People have been using herbs for medicinal purposes longer than the "medicines" that are used to treat today's illnesses. If it will help keep them worm free, then I'm all for it. I also chop up garlic tops and feed those as a...
I don't know if you can "overdo" it, but I just took a pumpkin and threw it on the ground so it would break in half. It took them a couple days to go through the seeds and another couple of days to eat the flesh.
I have to say though, it's not their favorite treat, so they wait til everything...