According to Jack Nicholson on a Playboy Magazine interview (April 1972), director Mike Nichols asked Nicholson and other cast members not to smoke marijuana while filming on location in Vancouver, British Columbia, where cannabis was easily available. Nichols thought that it dulled an actor's performance.
Jonathan: At one time, it was great what we had... the kidding around. It can't have a natural time span. Affairs can't dissolve in a good way. There's always got to be poison. I don't see why, I really don't see why!