The genre of music The Pierces identify as is Psychedelic pop, rock and folk. This is music that attempts to replicate or enhance the experiences of certain drugs. The use of the drug in the music video links to the genre and therefore makes it very clearly to the audience what the genre is. This is conventional to music videos. 

 

Moreover the audience who listen to this type of music are more likely to identify with this drug. So the mise-en-scene used is effectively representing the audience in the video.