Recreational drugs and alcohol actually increase neurogenesis or restore neuroplasticity, via increasing neurotrophins, such as BDNF, NGF, etc.

This is why people who say they are not "genetically predisposed to addiction" have absolutely no idea what they are talking about.

Any individual can become addicted to any number of substances, typically rooted in what corrects internal/epigenetic biochemical imbalance.

Neurogenesis implies reinforcement for continued substance consumption as you rewrite your brain.

Neurogenesis can go both ways, and this is why the importance of what you consume in diet, environment, media, and your very own thoughts in the neurogenic/accelerated learning state should never be understated.

It is also the reason psychedelic entheogens can have such a long-lasting traumatic impact on some susceptible individuals due to neurogenesis induction.

THIS is why recreational drugs and alcohol (caffeine, nicotine, refined sucrose, and cannabis included) induce addiction.

The upregulation and downregulation of receptor systems become set in place long-term until reversed or allowed to reach homeostasis once more with total abstinence.

Trauma itself has a similar function in the fact that it greatly increases glutamate and neurogenesis with it until GABA receptor system is downregulated and inflammation/oxidative stress is allowed to run rampant.

Regardless of whether or not you "feel" addicted or you have accepted you are addicted rather, chronic consumption of any substance induces physical dependence via these mechanisms.

And there's even some nuance here because it is the potency at which these common recreational substances induce neurogenesis that causes such issue, while the potency of the rest of the mechanisms is equally powerful enough to induce downregulation of receptors or "the high".