By Tom McKay

Scientists are increasingly sure that coffee -- without any sugar or milk -- is nowhere near as bad for you as commonly thought, and actually has a lot of health benefits. Now they're looking at its effect on regions of the brain associated with addiction, and finding some pretty weird stuff.

Researchers from the Integrative Neurobiology Section of the National Institute on Drug Abuse intravenously administered marijuana-addicted squirrel monkeys with THC (the primary psychoactive component of pot), after giving them varying doses of drugs that mimic caffeine's effect on the brain. The monkeys were then allowed to choose how much additional THC they would like pumped into their veins.

The results? Monkeys that had been given small amounts of the caffeine-mimicking drug were less likely to self-administer THC, while monkeys that were really amped up on the stuff chose to take more THC.

What gives? Dr. Gary Wenk explains on the Oxford University Press blog:

"Caffeine has only one known action in the brain; it blocks the neurotransmitter receptor for the chemical adenosine. Adenosine receptors live on both sides of synapses. ... What the scientists discovered was that blocking the presynaptic adenosine receptors caused the monkeys to stop self-administering THC. In contrast, blocking the post-synaptic adenosine receptors caused the monkeys to increase their self-administration of THC."

In other words, a little coffee hits the brain differently than a lot of coffee, and the results indicate something far stranger than just whether or not a cup of joe could help someone cut back on pot -- it actually suggests, Wenk writes, that "coffee's addictive properties also involve the brain’s marijuana-like neurotransmitter system."

While you were busy graduating from the occasional espresso to freshen up a bit in the morning to chugging it all day like Tweek from "South Park," caffeine may have been rewiring your brain just like pot does for heavy users. So it's not a coincidence you might find yourself fantasizing about a piping hot cappuccino throughout the day. Caffeine has gotten all up inside your head.

It's too early to say whether the same effect occurs in humans as it does in simian psychonauts, so if you think you have a problem with marijuana dependence, you should probably talk to a doctor, not a barista.