Substance addiction is a brain disease that corrupts choice-making; Stigma is a disease of the heart, that can be controlled by choice. It is a treatable disease and stigma severely compromises healing.
Addiction affects the mid-brain, the part that is concerned with keeping us alive for the next 15 seconds. It is pre-choice, pre-morals, pre-character, pre-personality, pre-will power. Drugs hijack the brain and our survival mechanisms. Craving usurps all reasoning. Suffering ensues. Simulate the feeling: try holding your breath as long as you can. The desperation for survival you begin to feel correlates to the craving for substances. The orbito-frontal cortex ceases to function properly. The neurotransmitters and receptors, especially dopamine, glutamate, and cortisol are all disrupted, corrupted. Anhydonia develops. Hypofrontality occurs. Memory fails. Only the substances matter. The personality is hacked along with all decision making. The difficult and disgusting, sometimes illegal, always alienating behaviors come from this hijacking - basically, it is the drugs running the show, not the infected person.
This would happen to ANY of us, it is merely brain physiology and anatomy. Not all of us are susceptible though, as about 10-15% of the population is. This genetic predisposition is unpredictable. Probably more than 100 genes are involved in different arrangements. Epigenetics contribute both to susceptibility and protection. The best research I read has spawned the current biopsychosocial theory of addiction which attributes about 60% of the weight on nature, our genetic biochemistry and brain neural network, synapses, and neurotransmitter physiology.
I am aware of many stories where substance dependence began with one use, often a pain prescription for an opioid. For some such a prescription makes them nauseous and foggy in a way that they don't take a second pill despite the pain. For others it does its job subduing the pain and makes them pleasantly sleepy. But for others, it "lights them up" in a profound and unexpected way that precipitates an abuse cycle. The world seems right and they comfortable in it for perhaps the first time. Studies show that 80% of heroin users started with an appropriately prescribed opioid that then became too difficult and too expensive to continue obtaining so they turned to the accessible and cheaper heroin. Some sampling of resources are listed on the next page. To explore them, click below.