Weed (also known as Marijuana, Pot, Dope, and Endo) is a drug that comes from the Cannabis plant. It appears in many games throughout the GTA series.
GTA San Andreas
Though weed is referenced in earlier games, it first appears in GTA San Andreas. It is seen during the mission Are You Going to San Fierro?, in which CJ must burn weed fields belonging to The Truth before authorities arrive, at the farm in Leafy Hollow. While the marijuana plants are burning, Carl is visibly affected by the resulting smoke, as the camera will start to sway and Carl will comment on how he is starting to get dizzy.
Ryder smokes weed laced with PCP, a mixture which he makes himself and calls "water". All gangs are seen smoking marijuana. Also, some pedestrians in Los Santos can be heard saying things such as "that ese put dust in my weed" and "where the weed at?".
There is also a mod which enables a feature that was originally going to be in the game, where CJ can get high on weed.
GTA IV and Episodes From Liberty City
During GTA IV, Little Jacob is almost always seen smoking weed during much of the storyline. His best friend and business partner Real Badman also frequently smokes weed. Most of Jacob's missions and jobs for Niko also involve weed.
GTA Chinatown Wars
Weed makes its first official interactive appearance in GTA V. It can be smoked using a bong by both Michael and Franklin. Michael and Franklin will get high and react to the effect. The Ballas have a marijuana growing/packing business set up in an abandoned sawmill just south of Paleto Bay. Smoke on the Water, a medical marijuana pharmacy, can be purchased by Franklin although he won't able to buy anything from the store. Marijuana plants can also be seen growing at Braddock Farm. The Grass Roots series of stranger missions center around weed; Barry, a man wishing to legalize the drug, meets Michael, Franklin and Trevor on separate occasions and wants them to sign his petition. He offers each of them weed, which Michael and Trevor reluctantly take and experience frightening trips as a result of the weed being laced with a hallucinogen. Franklin, however, doesn't experience the effects and chastises Barry for its low quality. Barry later has Franklin deliver two large shipments of weed to his apartment for use in a "smoke-in" protest at city hall. As it turns out however, Barry was lying about the protest and uses the weed for himself.
In GTA Online, weed functions the same way it does in GTA V. It can be smoked by using a bong if the player owns an apartment, or when visiting another player's apartment. The player will experience a blurry effect to simulate the feeling of being high.