Editing Heroin (section)

===Long-term effects===
[[File:Long-term effects of heroin.png|thumb|Long-term effects of intravenous usage, including – and indeed primarily because of – the effects of the contaminants common in illegal heroin and contaminated needles<ref name="ONDCP" />]]
Repeated heroin use changes the physical structure and physiology of the brain, creating long-term imbalances in neuronal and hormonal systems that are not easily reversed. Studies have shown some deterioration of the brain's white matter due to heroin use,<ref name=Hamp2019>{{cite journal | vauthors = Hampton WH, Hanik I, Olson IR | title = [Substance Abuse and White Matter: Findings, Limitations, and Future of Diffusion Tensor Imaging Research] | language = en | journal = Drug and Alcohol Dependence | volume = 197 | issue = 4 | pages = 288–298 | year = 2019 | pmid = 30875650 | pmc = 6440853 | doi = 10.1016/j.drugalcdep.2019.02.005}}</ref> which may affect decision-making abilities, the ability to regulate behavior, and responses to stressful situations. Heroin also produces profound degrees of tolerance and physical dependence. Tolerance occurs when more and more of the drug is required to achieve the same effects. With [[Substance dependence|physical dependence]], the body adapts to the presence of the [[drug]], and withdrawal symptoms occur if use is reduced abruptly.<ref name="National Institute on Drug Abuse" />