Galatians 5:21 Envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of God.
The ilegal drugs fallen under the line of drunkenness. Yes, weed is a drug that is suppose to help people to eat. When those who have eating disorders. But some people just abuse it. God would intervene if it gets to that point. Because God doesn't want people to use the good thing to a bad thing. Like for example, a woman who loves chocolate. She doesn't eat much. But when trouble rises, she would indulge on that chocolate and loses control, and ends up on diabetes, and other health issues.
It's the same thing with addictive drugs such as heroine, weed, and beer. It becomes a problem when you become tested. If your feeling like your being convicted. Because there is a trial coming to you, and God wants you to be ready for it. He wouldn't want you to be in darkness when He puts you under a test by "Storms of Life."