Not all marijuana works in the same way. And understanding the differences between the two major strains — indica and sativa — could play a crucial role in advancing the medical uses of pot over the next few years.
But even though marijuana has been a part of human civilization for thousands of years, we know surprisingly little about the two strains. Part of the problem is that the US government has made it notoriously difficult to study marijuana — since pot is a schedule 1 substance, it's considered to have no medical value by the feds, so they've been reluctant for years to allow much research on it. (Although that's beginning to change.)
Still, we do know a little about the different strains of marijuana based on anecdotal evidence from users. As the video above by Aaron Byrd and Axel Gerdau in the New York Times explains, indica tends to produce a relaxing body high, while sativa tends to yield a more energetic and euphoric high. And of course, the effects vary from person to person.
Why do these strains work differently? Scientists aren't really sure. THC is the main psychoactive compound in marijuana, and that's true for both the indica and sativa strains of marijuana. So perhaps it has something to do with how THC interacts with some of the many other chemicals in marijuana plants (what's called the "entourage effect"). But it's unclear which chemicals could be behind these different interactions — there are more than 500 active ingredients and 70 cannabinoids in marijuana, so it's not exactly easy to narrow down the list.
But these different interactions matter for medical uses of marijuana. If someone is suffering from depression, maybe an uplifting high from a sativa strain is the best medicine. If a patient is dealing with anxiety or pain, maybe a relaxing body high from an indica strain would be better. Figuring out all of this will likely be a big focus of the medical research of marijuana as the science evolves.