Try to guess the poster's message before reading below:
The goal was to make a dramatic poster utilizing positive and negative shapes. In the center there's a white H, a common term for Heroin. A skull and syringe make up the negative shapes within the H.
"Hit rock bottom, in attempts to get high" was chosen as a vague tagline.
"Hit" alludes to the action of taking a hit of heroin.
"Rock" is meant to hint at Black Tar.
"Bottom" and "High" were chosen as a play on words because they contradict each other.