There are very few scenes of graphic sexuality in Homestuck, though there are a decent amount of sexual innuendos throughout the webcomic.

There are some pretty gruesome scenes, which may disturb younger viewers, though the simplistic art style of the webcomic makes it more mild.

There are some violent moments where the art style changes itself up to emphasize the carnage and gore.

Homestuck often includes profanity. "F-bombs" are often dropped.

As far as I remember of the series, there is very little drug use in Homestuck. One of the only things drug related in the series is a drug used by the alien species, trolls, which is very obviously similar to marijuana. In the webcomic, there is also a good amount of alcohol use by certain characters.