According to the article "Addiction to Music Has Biochemical Basis" on Softpedia News by Tudor Vieru, which reports on findings by Robert Zatorre and Valorie Salimpoor (Salimpoor & Zatorre, 2013), who both hold appointments as neuroscientists at the McGill University:
"listening to music you like also triggers the release of dopamine, a neurotransmitter that plays a role in underlying pleasurable reactions caused by food, drugs and arousal before intercourse"
"The chemical has been linked in a variety of studies with mechanisms underlying addiction in humans, and it would appear that it also plays a role in the way people feel when listening to their favorite tunes."
"Dopamine is important because it makes us want to repeat behaviors. It’s the reason why addictions exist, whether positive or negative,”
"the euphoric ‘highs’ from music are neurochemically reinforced by our brain so we keep coming back to them. It’s like drugs. It works on the same system as cocaine,"
"It’s working on the same systems of addiction, which explain why we’re willing to spend so much time and money trying to achieve musical experiences,"
References
Salimpoor, V. N., & Zatorre, R. J. (2013). Neural interactions that give rise to musical pleasure. Psychology of Aesthetics, Creativity, and the Arts, 7(1), 62–75. 10.1037/a0031819 Free PDF available at: https://pdfs.semanticscholar.org/f818/f3a9db17e3defb250a0c00ff64b4c4631376.pdf