While it is technically possible to get high off of second-hand marijuana smoke, the chances of that happening are unlikely at best. That's because cannabis smoke doesn't contain very much THC - the chemical that produces the plant's characteristic high.
When you smoke a joint, roughly half of the THC is absorbed into your body. That means the THC content in the smoke being exhaled has already been significantly reduced. And since you're probably not letting someone blow smoke directly up your nose or throat, the chances of breathing in enough THC to get high are slim.
But that doesn't mean it can't happen. Hot-boxing is a legitimate thing, according to science.
Studies have shown that putting people in a confined space where cannabis is being smoked will see the non-smokers develop signs of being mildly impaired. However, when placed in a space that had better ventilation, the non-smokers only had tiny amounts of THC in their blood. So you can get a buzz from being hot-boxed, but it won't be nearly as strong as smoking a joint yourself. Unless, of course, you're a dog or cat.
Because cats and dogs weigh significantly less than humans, a little bit of THC can have a big effect on them. That means they can get much, much higher from second-hand smoke. And while medical marijuana offers many health benefits for pets as well as humans, you don't want your four-legged friend to get uncomfortably high, so be careful when having a joint around your pet.
h/t: The GrowthOp