opioid

Opioids are the heavy artillery of pain relief: a class of drugs that act on the body's own opioid receptors to blunt severe pain. The name comes from opium, the dried juice of the poppy, but the family today includes natural compounds like morphine, semi-synthetic ones like oxycodone, and fully synthetic ones like fentanyl. What unites them is the receptor they engage, not where they come from.

These drugs mimic the body's natural pain-dampening molecules (endorphins and enkephalins). By activating opioid receptors in the spinal cord and brain, they reduce the transmission of pain signals and change the emotional reaction to pain, so that pain that remains feels less distressing. The same receptor activation, however, also produces euphoria, slowed breathing, constipation, drowsiness, and pupil constriction.

Opioids are extremely effective for acute severe pain, cancer pain, and end-of-life care, and there is no fixed dose ceiling — the dose can be increased as tolerance develops. Their great danger is that the dose which stops breathing is not far above the dose that relieves pain, and repeated use leads to tolerance, physical dependence, and the risk of addiction. The opioid overdose crisis is a direct consequence of these properties, which is why prescribing is now far more cautious and why the antidote naloxone is kept close at hand.