Heroin has a number of effects on the brain. The drug binds to parts of our brain cells called opioid receptors, blocking pain and generating feelings of well-being.
Severe itching is a well-known side effect of most opioids, including heroin. It may be a sign of chronic heroin use or a heroin overdose. Until recently, scientists weren’t exactly sure why opioids make people itch.
Recent research indicates that the phenomenon is related to at least two mechanisms — the release of immune-system chemicals called histamines and the activation of special “itch-specific” receptors in the spine.
Heroin is an illegal drug made from morphine, which comes from the sap of the opium poppy plant. Like other opioids, heroin produces a euphoric rush when it’s injected, snorted or smoked — and it’s highly addictive.
A person can become addicted to heroin within a short period of use. Some people begin using heroin after becoming addicted to opioids, such as OxyContin, Vicodin or Percocet.
While heroin produces pleasurable feelings, it also causes a number of uncomfortable side effects, including severe itching. Other symptoms and signs of heroin use include nausea, vomiting, warm flushing of the skin, constricted pupils and profound drowsiness.
Not everyone who uses heroin will itch, but many people do. This itching can be so severe that people will scratch and pick at their skin until it scabs and bleeds.
Heroin and other opioids appear to cause itching in at least two ways.
Heroin triggers the immune system to release histamine, a chemical that narrows blood vessels. The drug also irritates nerve fibers that cause itching. Histamine is normally released when a person has an allergic reaction, which is why so many allergies cause itching.
A 2014 study published in the journal Substance Abuse Treatment, Prevention, and Policy noted that histamine levels in chronic IV opioid users were three times higher than those of healthy individuals who don’t use heroin. Opioid-related itching is not considered to be a true allergy, however, because it doesn’t activate the entire immune system. Instead, it’s considered a “pseudo-allergic” reaction, according to an article published by HPS Pharmacies.
Heroin and other opioids also appear to bind to special receptors in the spine that trigger severe itching, according to a 2011 study published in the medical journal Cell.
Interestingly, Zhou-Feng Chen, director of the Center for the Study of Itch at the Washington University School of Medicine in St. Louis, Missouri, and his colleagues demonstrated that this itch-specific receptor, known as MOR1D, appears to operate independently from receptors that relieve pain.
When they blocked the receptor in mice receiving morphine, the mice no longer scratched. The mice did, however, still experience pain relief from opioids.
“There are more than a dozen forms of the opioid receptor on nerve cells, but MOR1D is the first one that has nothing to do with killing pain. It only transmits itch,” Chen explained in a 2011 press release by Washington University.
Some people who are addicted to heroin and other opioids pick their skin. The picking can become so severe that the person bleeds and develops scabs and scars.
Compulsive skin picking has many scientific names, including dermatotillomania, psychogenic excoriation and neurotic excoriation.
In addition to substance abuse, the condition is commonly associated with several psychiatric conditions, including obsessive-compulsive disorder, eating disorders, borderline personality disorder, kleptomania (compulsive stealing) and body dysmorphic disorder.
It’s not just opioids that cause skin picking. Stimulant drugs such as cocaine, crack cocaine and crystal meth can also cause the compulsive behavior. Combining cocaine and heroin to make a speedball may make the effects even worse.
Itching and skin-picking usually stop when opioid use is discontinued.