Most of the United States spells marijuana as I just did. But if you live in the state of Michigan, you may have noticed some official documents spelling it like "marihuana." If you're wondering why, we can help you out.
In 1937 Congress passed the "Marihuana Tax Act" that essentially made it illegal to buy or sell cannabis. At the time, "marihuana" was the more commonly used spelling of the drug, while "marijuana" didn't come into vogue until years later.
When Michigan began passing laws related to cannabis, they continued using the "marihuana" spelling since it was technically the official spelling used by the United States government. And since every previous marijuana law used the "h" spelling, the state simply continued to do so as well.
There isn't any effect of the "H" spelling. While official documents and licenses contain the "H" spelling, cannabis businesses aren't required to do so and are free to use the "marijuana" spelling we're all used to.
Interestingly enough, marijuana was really just a slang phrase in the 1930's used to describe cannabis. Congress' law is what essentially made marijuana the official word for the drug. So naming the bill "Marihuana" in 1937 would be equivalent to Congress passing a law with "Pot" in the title today.
(h/t Detroit Free Press)