Thompson was also an ardent supporter of drug legalization and became known for his less-than-shy accounts of his own drug use. He was an early supporter of the National Organization for the Reform of Marijuana Laws and served on the group's advisory board for over 30 years, until his death. He told an interviewer in 1997 that drugs should be legalized "[a]cross the board. It might be a little rough on some people for a while, but I think it's the only way to deal with drugs. Look at Prohibition: all it did was make a lot of criminals rich."
After the September 11 attacks, Thompson voiced skepticism regarding the official story on who was responsible for the attacks. He speculated to several interviewers that it may have been conducted by the U.S. Government or with the government's assistance, though readily admitted he had no way to prove his theory.
In 2004, Thompson, regarding politics, wrote: "Nixon was a professional politician, and I despised everything he stood for—but if he were running for president this year against the evil Bush–Cheney gang, I would happily vote for him."