Marijuana was a type of drug that was made from a certain type of Earth plant. It was green in color, and usually the drug was rolled up into a joint or blunt, it is then lit, and then smoked, in the same manner that tobacco is smoked.
When Oliver Queen was on Starfish Island, he used a drug that appeared to be marijuana, although he himself was uncertain what it was, yet he did wonder. He rolled it up into a blunt and then smoked it, hoping it would calm his nerves. He described the drug as "potent."