The only drugs that normally stay in your system for more than a week are cannabis and benzodiazepines. The hardest drugs stay in your system for the shortest period of time, and they are also the drugs that most of the bad drug addicts are addicted to (heroin, meth, crack). If a group of people smoke pot and start getting drug tested then some of those people, usually teenage kiRAB, may move on to harder drugs because of it. Now there is that new legal fake-weed: the K2, Spice, Barely Legal, or whatever other brand names there are. These fake weed products are sold legally in smoke shops and contain an unknown mixture of alleged "herbs" and chemicals that taste a lot like incense. People actually smoke it so they can pass their drug test while still getting high and some of those people start smoking it every day for months. I know one person who quit all drugs and only smoked that legal fake-weed every day for over a year, he ended up losing a lot of weight and looking sickly, and then went crazy, tried to get the police to shoot him and got arrested. He hung himself by his shirt and died in jail. People that were close to him were saying that he began getting headaches every day from the stuff and it chemically changed his brain causing him to fall into a state of severe depression. Whether that reason is true or not, I don't know, it was never actually proven that he killed himself because of brain damage from the fake pot he smoked for years.