Drug that relieves pain without blocking nerve impulse conduction or markedly altering sensory function (see nervous system ).
Two classes are defined by the type of pain-relieving action. Opioids (opiates and synthetic narcotic s; see opium ) act on brain receptors to inhibit pain impulses. They may be used for short-or long-term pain relief, usually by prescription, but carry a risk of drug addiction . Nonopioids, used mostly for short-term relief and modest pain, are available without prescription. They include aspirin and ibuprofen ) and acetaminophen ; all act by inhibiting synthesis of prostaglandin s, molecules involved in the peripheral perception of pain.