Continuous compulsion to use opioids despite physical, psychological or social harm due to the use
Aetiology
Opioids are a class of drugs that include the illegal drug heroin, synthetic opioids such as fentanyl, and pain relievers available legally by prescription such as codeine
Pathophysiology
Opioids are either a natural derivative of opium or a synthetic substance with agonist, partial agonist, or mixed agonist and antagonist activity at opioid receptors
A natural high or a drug induced high is mediated by the mesolimbic dopamine pathway - sometimes referred to as the pleasure centre of the brain, with dopamine as the pleasure neurotransmitter
Clinical features
Opioid intoxication
Drowsiness
Confusion
Decreased respiratory rate
Decreased heart rate
Constricted pupils
If the substance, such as heroin, has been injected, there may be evidence of needle marks abscesses or vein collapse at injection sites