Alcohol and drugs are consumed in continuously and in significant amounts through most of the film.
Drugs and drug use are a big part of the film, including abuse, smuggling, and adverse effects, all played for laughs.
In one sequence, a character is pressured by a second character to smuggle a balloon containing drugs in his rectum. The first character phones his boss for support in refusing, but the boss orders the person to comply. The character is shown placing the balloon in the back of his pants, and we see his facial expressions as he inserts the balloon. The balloon and drugs within it are constantly referenced until, a few sequences later, the second character forcibly retrieves the balloon in a bathroom (on camera, but behind a screen; we see this action in silhouette). However, before the second character can use the drugs, the first character deliberately bursts the balloon, spills the powder on the floor, and grinds it into the carpet to prevent its use.
The character of Aldous Snow is a relapsed abuser of alcohol and user of drugs, including heroin. He frequently pressures another character into reluctantly joining him in alcohol and drug use. In one sequence, the other character imbibes to excess to prevent Aldous from getting too impaired to perform. Some may believe that Aldous is an addict, and based on his behavior in the film, that could be argued. However, at the beginning of the film he has been clean for seven years; he returns to drugs and alcohol out of spite towards another character (not out of weakness); and he, arguably, appears to function both with and without drugs and alcohol. And, despite heavy use of drugs and alcohol, Aldous is never shown to suffer any true withdrawal symptoms (other than, perhaps, irritation over losing some drugs) when he is not using.
In the middle of the film, Aaron smokes a 'jeffrey,' which is then revealed to be a combination of many drugs. After smoking it, Aaron believes he is about to have a heart attack.