I recently read a book called, I believe, This is Your Brain on Music or something similiar. It was written by a studio producer/session player who became a psychologist who studied the effect music has on the brain.
Anyway, in one part of this book, there was reference to an experiment done. The experiment involved a drug called Naltrexone. This drug is commonly used to "bring someone out of an opiate or opioid overdose" (it does this by acting upon opiate receptors stronger than any recreational opiate, thusly pushing the drugs off of the afflicted receptors in your brain). When a person is under the influence of Naltrexone, they are unable to get high on opiates/opioids, because the Naltrexone binds stronger to the the receptor sites, so if they take the drug it basically passes though the body unmetabolised and inactive psychologically.
The experiment detailed earlier in the book was interesting; normal people (I.E., non-addicts, clean people) were given Naltrexone and a great majority, some 90% I believe, found that they were unable to enjoy music while loaded up with Naltrexone. This was eventually determined to be caused by the fact that the parts of your brain that process music (especially the parts of your brain that let you enjoy music) are the same parts of your brain the process opiates and opioids (which are the pharmaceutical category for drugs like Morphine, Heroin, Oxycodone, Fentanyl, Methadone, etc., etc.). When this part of the brain is blocked (trying to stop opiate abuse or prevent overdose), it was basically not enjoyable to listen to music, just as it was not enjoyable to take opiates/opioids.
I couldn't believe the study hadn't been published or discussed earlier, as it basically had and answer for the question that my friends and I have asked many times, "Why are so many great musicians junkies?"