Many many people don't start with heroin, nor do they turn to drugs for the reasons you cite. They start with back pain due to a workplace injury, for which a

Many many people don't start with heroin, nor do they turn to drugs for the reasons you cite. They start with back pain due to a workplace injury, for which a doctor immediately prescribes them a powerful opiod (and perhaps a companion drug to deal with the resultant constipation). Because it's "medicine", these people don't fully understand the risk of addiction nor do they recognize the signs of addiction and tolerance as they develop. Meanwhile, the doctor shirks their duty by not remaining in constant contact with the patient to manage any dependency should it occur. These individuals eventually become addicted because the drugs lose efficacy over time (and in the case of Oxy, don't actually work for as long a period of time in the body as claimed, forcing people to up their own dosage). And thus the spiral of addiction begins. Because of the lack of public awareness and the shame and stigma of addiction, people don't seek out help. Instead they try to manage the problem themselves. Ultimately, once addicted they turn to street drugs because they're a) cheaper, and b) more readily available.