Harrelson, who's co-starring in The Hunger Games: Mockingjay - Part 1, made his first appearance on SNL since 1992 (he also hosted in 1989).
During the monolgue, he was joined by Jennifer Lawrence, who fumbled a line about him getting high all the time and ad-libbed, "You're always so stoned." About a minute later, Harrelson conceded, "I smoked a lot of herb before I came here tonight."
A follow-up skit ("A New Day," watch below) focused on New York City's new marijuana decriminalization policy, with cast members in unision hitting the streets with 25 gram bags, then getting stopped by cops when Pete Davidson tries to light one up. There are several Funyuns references - a banner at the rally and bag in Diamond's apartment.
Dressed up in hippie garb and holding a plastic purple bong, Harrelson climbed atop a car and exclaimed, 'Free at last!'
Michael Che also did a pot joke on Weekend Update, regarding his own use and SNL boss Lorne Michaels.
In another skit, Harrelson sat in a bar with three male cast members reminiscing about the '80s. He kept bringing up crack.
Kendrick Lamar was the musical guest.
Diaz, who's co-starring in the film adaptation of Annie, will be making her first appearance on SNL since 2005 (she also hosted in 2002 and 1998). Bruno Mars and Mark Ronson are the musical guests.