A lot of controversial information is known about Crowley and when anyone mentions his name, people frequently mention his addiction to heroin and opiates. Like this was the cover that hides all his successes, qualities and truly iron dedication to the occult.
The problem is that Aleister Crowley was many things, but not a druggie. Opiates (including heroin) weren't illicit drugs in his time, they were drugs prescribed by doctors for the cure of things like asthma, stress, depression, diarrhea. It was much later when medical society recognized heroin's side effects as too horrible to be an official cure, but some anti-diarrhea drugs still contain a minimal amount of heroin.
Crowley also mentioned his addiction quite frequently in his notes, he used heroin for a longer period of time, so he was very addicted to it on a physiological level. According to his notes he was trying to fight this addiction on a regular basis, but heroin is a very horrible enemy of the will when it comes to side effects. The will was also one of the reasons why Crowley fought his addiction, he did believe that anything that controls or limits your will should be gotten rid of. Unfortunately his addiction was too strong, he didn't free himself from the drugs for his entire life.