Analgesia

Analgesia is the reduction or absence of pain sensation without loss of consciousness, produced by the body's own systems, by medicines or by other interventions.

The body contains built-in analgesic pathways. Descending signals from the brainstem release opioid peptides, serotonin and norepinephrine in the spinal cord and dampen incoming pain messages, which explains why pain can fade during intense exercise or emergency. Medicines borrow these mechanisms: opioids act on the same receptors as the body's endorphins, nonsteroidal anti-inflammatory drugs lower prostaglandin production at the site of injury, local anesthetics block nerve conduction, and some antidepressants and anticonvulsants reduce nerve-related pain by altering signaling in the spinal cord and brain.

In research, analgesia is measured as a change in a pain score from baseline, as the time until a stimulus becomes painful in laboratory tests, or, in animals, as a change in withdrawal reflexes and behavior. The word describes an effect, not a specific drug, and it is distinct from anesthesia, which removes all sensation. Analgesic effects are also strongly shaped by expectation, which is why placebo control is essential in pain trials. The endocannabinoid system participates in pain modulation, and cannabinoids have been studied for analgesic effects in animals and people; clinical findings are mixed and no cannabidiol product has an approved analgesic use.