Marijuana / Marihuana are descriptors appearing in legal documents, such as Michigan Medical Marihuana code / laws, so my own humble opinion is that elevates the word(s) beyond slang. Cannabis, by contrast, does not appear in the code. But does that really matter in our little friendly discussion?
The topic at hand is whether hemp, used commercially all over the world for clothing, rope, etc is essentially the same genus & species as what we smoke. Right? Well, what we call “hemp” is (specifically) Cannabis Sativa. Or so it appears in laws & legal docs across the us.
That’s my humble 2c, & yours is equally welcome.