One character is convinced that he is hallucinating and paranoid due to his friends lying by omission. It is eventually all figured out and he knows the truth.
Among smaller instances, the main character eats the brain of an alcoholic (S1:E10) and is shown abusing alcohol for that period of time. Also, alcohol is a very common theme throughout the show in the form of social drinking/coping via alcohol/etc, even in non-addiction contexts, which is something to be aware of if you struggle with alcoholism.
S1:E10/E11 take place in a mental institution after a main character willingly institutionalises themselves, and another patient at the hospital is found dead. Aside from a few "crazy people" remarks, there isn't much explicit ableism or mistreatment. This event is mentioned a few times throughout the show outside of these episodes.
Not a complete yes but close enough to be potentially triggering: In S2:E9 a girl is shown attempting suicide via gunshot, but is stopped. In S1:E11 a murder is framed as a suicide via wrist injury. In S1:E10 another character's death is ruled a suicide, but it's a cover up.
In one episode, later in the show, a sexual relationship between a teen girl and her stepdad is mentioned, but it is just a small part of the one episode