Marijuana hasn't been medically proved to help many of the things people claim. There is medical evidence of helping cancer patients eat, small pain management, and possibly helps with epilepsy.
Everything else hasn't been researched. Marijuana can be addicting as it releases chemicals in the brain that the brain takes a liking to or relates whatever trigger to the urge to release that chemical again.
Also their is many uses for cannabis without smoking it. Alchohol was used in the new Testament but drunkenness was forbidden. If something is mind altering and you are abusing it for that purpose like taking a pain killer just to feel high then yes that is sin.
There is a good Christian organization
https://learnaboutsam.org/
that is fighting the new Big Tobacco rise but instead called Big Marijuana rise of the tobacco industries taking control over the cannabis markets making still many people getting their weed from the black market. Two adult deaths have possibly been linked to edibles and a Colorado children's hospital said it has seen an uptick in the number of admissions of children who ingested marijuana-laced foods
Still not much research has been done on affects of brain cells. But from personal experience by being around pot heads in school. They never was like their old self again. And not very productive while being high.