Is Marijuana a Gateway Drug? Full disclosure here. My grandfather Johnnie Carter who I have a lot of respect for, was also a heroin addict. My grandfather, on the streets of Harlem New York, did all the horrible things to his family that addicts do. Stealing and so on, but at the end of the day I’m proud of my grandfather because when he died, he died clean, and had kicked his tough addiction. To me, it’s a no-brainer of whether marijuana is a gateway drug. Of course it is.