At first glance, yoga and marijuana seem made for each other: They're both commonly described as being “relaxing,” practitioners of both like to make outrageous claims about their medical efficacy and the cultures of both are rife with people who smell like patchouli. But there's an odd rift in the yoga community over whether the two should be mixed or not. (It's the calmest, most chill rift you'll ever encounter, but we'll count it anyway).
The controversy has only gathered steam since Washington and California (arguably the most patchouli-drenched states in the Union) legalized cannabis. Suddenly, a few yoga studios started offering marijuana-friendly or even -oriented classes and experts started to question if this was just another marketing technique to cash in on the Green Rush. Others attacked the practice, claiming the psychotropic effects of cannabis were at odds with the very heart of yoga—the unity of mind, body and spirit. A common argument against the combination is that “clarity” and “mindfulness” are somehow derailed by cannabis use.
I would hazard the guess that those people have either never tried marijuana, or they aren't familiar enough with it to get past the initial novelty of the experience.
It's funny, because there's a pretty solid tradition of cannabis use connected to the mystics of Hinduism going back centuries. The term “indica” comes from the classical Latin word for “of India.” During the Hindu “festival of colors,” Holi, celebrants drink bhang—a marijuana-infused drink associated with the god Shiva, the use of which dates back to at least before the Vedic age (1500 to 500 BCE). Cannabis also plays a major role in the famous “Churning Ocean of Milk” cosmological myth and is considered by sadhus—Indian mystics—to be one of the five sacred plants given to humans by the gods. Another notable use of marijuana in India (along with alcohol, excessive sex, self-mutilation, coprophagia and cannibalism, supposedly) is as an ecstatic vehicle among the Aghori, a sect of sadhus who attempt to reach enlightenment by exploring the darkest aspects of existence.
These are all extreme examples, of course, and don't necessarily characterize the practice of yoga in India, but they do give a certain precedence to the idea. And personal anecdotes from those who have tried crossing the two paths sounds more than promising. Many reported more focused yoga sessions characterized by a quiet mind.
But maybe most importantly—the idea makes sense to anyone familiar with the effects of cannabis. That's because almost every experiential marker associated with marijuana (even the bad ones) can be spun as aspects of “mindfulness”—a heightened awareness of sensory input and the body, concern over how others view you, an increase in openness, a sense of flow. Even on paper it sounds like cannabis and yoga were made to enhance each other.