It's the Buy-One-Get-One-Free special stores don't advertise: Buy some chicken, get some meds for free.

And just to make it more convenient for everyone, the drugs aren't in their own package -- they're already inside the chicken.

Chickens raised on factory farms are being fed everything from banned antibiotics to painkillers -- and some are even poisoned with arsenic -- all in the name of raising the fattest and pinkest possible birds in the shortest possible time.

Now, two new studies on chicken feathers (which hold traces of drugs and other toxins fed to the birds) show just how many meds are pumped into them -- and remember, whatever that chicken eats is what ends up on your plate on Chicken Night:

Caffeine: You know people who seem to eat every waking minute, right? Chickens are like them. Keep them awake longer, and they'll eat more and get fatter. But caffeine also makes chickens jittery (just like it does to some people), and since jittery chickens have tougher meat, they need something to help them to relax before they turn into tough old birds.

Prozac: One feather-meal sample from China found this antidepressant, and it's almost certainly there to help counter the caffeine and keep the chickens relaxed so their meat doesn't get leather-tough. And it's not the only drug that can have that effect.

Benadryl & Acetaminophen: These drugs turned up in the U.S. samples, and not because the chickens have allergies or need pain relief. It's because, like Prozac, these drugs can also relax the chickens and help keep the meat tender.

Antibiotics: Factory farm chickens are kept in such cramped and filthy conditions that illness is a much bigger threat than the wolf ever was. So the birds are drugged to preemptively protect them from a rapidly spreading infection -- and, conveniently, the drugs also help them to gain weight. The researchers found a class of antibiotics banned from poultry... but it looks like that ban is about as strong as a rubber chicken.

Arsenic: It's crazy, but this is actually allowed. Arsenic kills two birds with one stone (so to speak) because it kills bacteria and keeps the meat nice and pink. The problem, of course, is that it's arsenic -- and when you eat a bird fed this poison, you're getting a little dose of poison yourself.

It's enough to keep chicken off the menu for good, but you don't have to go that far. Just go organic instead.

And for more on food ingredients and additives -- including a few you just won't believe -- keep an eye on your inbox on Sunday for my Weekend Roundup.