There's a reason we love reaching that runner's high: The euphoria you get while pounding the pavement is not only real, it's as good as the high you get from a drug, according to two new studies.

This is thanks to two main kinds of opioid receptors. The first is mu-opioid reward receptors (MORs), which is responsible for releasing the pleasure-inducing chemical dopamine in both rodents and humans. Researchers at the University of Missouri Columbia looked at the reward center in the brains of two kinds of ratsone that was bred to be lazy and one that was bred to crave that running wheel like you crave your Saturday morning spin class. The active group actually had four times as many MORs in their brains and, after comparing the brain activation of both groups of rats, the researchers found that a great cardio session stimulated MORs the same way super addictive drugs like cocaine do.(Learn about Your Brain On: Long Runs.)

Just like the rats, some humans have more MORs than others, which explains why some of us are more prone to love a good sweat session (or why some struggle with drug addiction)-our brains are wired to crave the stimulation more, says the study's lead author Greg Ruegsegger, a doctoral candidate at the University of Missouri Columbia. Moreover, this research can also help with recovering drug addicts: Since the brain responds so strongly to the flood of exercise-induced endorphins, working out might actually be an effective treatment for drug addicts, the researchers hypothesize. Talk about a healthier high!

That's not all there is to a runner's high though. In another new study, researchers at the University of Hamburg and the University of Heidleberg in Germany found running also produces a chemical that stimulates your cannabinoid receptors, which, you probably guessed, are what respond to marijuana. Researchers found that running increased mices' pain tolerance while also decreasing their anxiety-the same side effects you can get from a little Mary Jane. (The New Runner's High: How Smoking Weed Affects Your Running.)

So if exercise looks a lot like drugs to your brain, can it be just as dangerously addictive?

According to Ruegsegger, the answer is a resounding yes. Exercise addiction is even listed in the DSM, the official medical encyclopedia of psychological disorders. But there's a fine line between being a fitness fiend and an actual exercise addict. According to the official definition of behavioral addicitions, exercise addiction is characterized by tolerance (you need to up your miles in order to feel the same buzz), withdrawal (you freak if you have to miss a day at the gym), intention effects (you start cancelling brunch with your besties so you can go to the gym), and lack of control (you can't bring yourself to skip spinning even if you want to). (Find out How One Woman Overcame Her Exercise Addiction.)