I'm not certain why it'd be a sin, there's a great chance that God created it as it is a medicinal plant.
I think it's got a bad wrap over the years. It has been a federal crime for a long time, but some say is it because it has drug potential when abused or that people can heal their bodies with it or both? I know a lot of states have made it legal and this is always burning both ends of a rope. You're gonna have your, "I wanna be stoned out of my mind," crowd and, "I need this to survive medically," crowd.
I don't believe cannabis is a sin itself. I do believe it can become sinful when a person is using it to purposefully harm their body and their habit harms their life or their family in some way.
On a medical perspective, it's been a miracle for me and has saved me many hospital trips and taking heavy benzodiazepines that make me feel awful for days after. Some guy gave me some to try because his mom has epilepsy like I do, and we cleaned his house so it was our tip for the day and that's the type of business he runs (it's credible, though. He's got licensing and everything for it).
I couldn't believe it. My arms started tremoring or the room felt like it was spinning faster than any carousel I'd ever been on - so fast that I couldn't walk without falling. I'd chew a bud of it, I don't smoke it. Yes, it's awful tasting. It was a low THC, high CBD strain, which is what I need. Within 5 minutes, the tremors stopped and the vertigo was becoming less and less. Within 10 minutes, tremors and vertigo and other unpleasant symptoms like vertigo are gone. Within 20-30 minutes, I'm recovering, and I'm aware enough in my mind to talk and answer questions and get up and perform a task if I absolutely have to. This is safer for me and my family as it's at home and the fastest treatment ever. It beats letting symptoms get worse en route to the hospital and then being drugged up with benzo's and not being able to walk for a few days and being insanely tired.
I was glad that recreational and medical use become allowed here as I didn't have to pay $150 for a medical card, although I know it has it's own benefits. Now, if we move like we hope to in a few years, it will only be available medically so I'd probably have to get the card and see what's available. Although, I try to work on other things in my life like diet and such to increase my chances of not having to use it.
I believe it's the intention that shines light on whether God would be good with it or not.