Drugs are an important part of Disco Elysium, even if you choose not to take them. As Robert Kurwitz's latest devblog at Estonian ZA / UM indie studio says, full sobriety is a challenge "favored by our writers" and "After all, there is no temptation without restraint." Curwitz then points out the many ways that Disco Elysium tempts you.
Here's one: drugs make you better at things. Each of the four statistics is drug related, with amphetamines temporarily improving your motor skills, for example. This means that it also improves any motor skill and maximum cap to which the skill can be raised. An hour later, the effect weakens, but if you used the opportunity to spend a point to increase the skill to a temporary maximum, that point is not lost. As Kurwitz puts it, "it started out as a glitch, but we kept it because testers liked it."
One thing I didn't realize during the game was that even though legal substances such as alcohol and cigarettes were always seen in the world to tempt you, illicit substances are hidden until you try some other way (for example through dialogue). Speed retention and pyrrolidone, the fictitious anti-radiation drug Disco Elysium that improves your state of mind, becomes visible only after you understand what to look for.
If you're already playing Disco Elysium and aren't worried about some small mechanical spoilers, like the effect of certain thoughts you can equip in your Thought Room, this deep dive into drugs is worth the read. Kurvitz also notes that trade names of substances have no effect, since "Like in real life, brands do nothing."
Because drugs give mechanical bonuses (and also have significant negative effects, to be fair) , this is a great disco Elysium passed it along the Classifications Council here in Australia. A quick search of the classification database does not show it, perhaps because it is not submitted for evaluation. Several members of the Governing Council have voiced their belief that the rules they are bound to follow are overdue for change, but without the cooperation of our lazy and conservative state governments, this will not happen. In the meantime, I guess everyone is looking the other way ̵