It was especially associated with black musicians. rev. Gary Davis first recorded the song Cocaine blues. He claimed to have learned in 1905. Musicians in the jazz and blues fields were not seen as members of high society (pun intended), and were known to be involved in other more nefarious endeavors. For instance Memphis Minnie engaged in prostitution or Lead Belly famously assaulting and killing multiple people.

Willie the Weeper, another drug song covered by Louis Armstrong, was most likely written in 1904 (it was more famously reworked as Minnie the Moocher by Cab Calloway). It has likely been associated with music for a long time... Drugs, artists, and creative works have been associated with one another for about as long as there have been drugs. However I think your question deals with how long has some popular music been explicitly about drugs. For this, look to the blues. When slavery ended blacks were not welcomed into white culture; they had to create their own culture (or perhaps, more accurately continue to grow their culture in a new setting of pseudo freedom). For this, they used the blues, not following the standards of white music either in structure or subject matter. Gospel music was for the church going crowd, blues for the Saturday night crowd. These songs would often be bawdy, about sex, drugs, etc. Even the word "blue," as in a comedian working "blue," is derived from this term. Eventually, as society becomes more progressive and more liberal, these drug references are even used by the "respected" musicians, and are more often recorded.

The short answer to your question: musicians have been doing drugs for a lonnng time, but after slavery there was a musical form that embraced this culture. Some white musicians especially in the country and folk genres took to this early (think Woody Guthrie) , but it was really black musicians generating this in the later part of the 19th century.

Most of my source for this is: Paul Oliver- Blues fell this morning