For a true musician, music is life. Ideas for songs are constantly coming to you, you notice the music and sound environment everywhere you go, instruments and music technology are a major financial investment in your life and a majority of your friends are also musicians. A consummate musician will live, eat and sleep music until they get it out of their system, onto a recorded track and share it with the world.
Musicians and addiction frequently go together because the same angst, energy and intelligence that prompt a person to be a musician are frequently the same qualities that spawn an addiction. Musicians are often a delicate combination of emotion and intelligence. In fact, many musicians are emotionally volatile, and instead of expressing their heightened emotions through communication, they express their feelings through music. Music is a healthy and productive outlet for emotions.
There is no activity that humans perform that has been found to use more of the brain at once than music. The learning and performing of music utilizes many compartments of the brain simultaneously, requiring the linear thinking of music theory, the creative thinking of composing, the hand-eye coordination of learning how to manipulate the instrument and the muscle memory of playing the instrument well, as well as many other subtle brain ability tests.
Sadly, substance abuse and addiction can also give the initial feeling of emotional relief to a person who is seeking it. Drugs and alcohol especially give the user an altered perception that can temporarily remove them from their emotions. This is the primary reason that musicians and other artists abuse substances or grow addicted to them. They come to depend on the temporary relief they provide, but have to continuously use them heavier and heavier so they do not grow tolerant to them. This presents an interesting conundrum to musicians. Should they labor over the composition of music when there is potentially no livelihood in it just to have a healthy emotional outlet? Or should they turn to mind-altering substances for pleasure feelings and not have to do any work? The answer is obvious to a healthy person but confusing to an emotionally unstable person.