An analgesic (colloquially known as painkiller) is any member of the diverse group of drugs used to relieve pain. Analgesic drugs include the nonsteroidal anti-inflammatory drugs (NSAIDs) such as the salicylates, narcotic drugs such as morphine, and synthetic drugs with narcotic properties such as tramadol. Other classes of drugs not normally considered analgesics are used to treat neuropathic pain syndromes; these include tricyclic antidepressants and anticonvulsants.

NSAIDs such as aspirin, naproxen, and ibuprofen not only relieve pain but also reduce fever and inflammation. Narcotic analgesics such as opiates and opioids largely work through specific opioid receptors in the central nervous system and alter the perception of pain (nociception). They are used to alleviate pain not relieved by the NSAIDs.

Tetrahydrocannabinol and some other cannabinoids, either from the hemp plant or synthetic, have analgesic properties.

Other analgesic agents include Ketamine (an NMDA receptor antagonist), Clonidine and other alpha-2 receptor agonists and Mexiletine and other local anaesthetic analogues.

Analgesics are frequently used in combination, such as the paracetamol (acetaminophen) and codeine preparations found in many non-prescription pain relievers. They can also be found in combination with vasoconstrictor drugs such as pseudoephedrine for sinus-related preparations, or with antihistamine drugs for allergy sufferers.

Safety

When used appropriately, narcotic analgesics are safe and effective, carrying relatively little risk of addiction. In the United States in recent years, however, there has been a wave of new addictions to prescription painkillers such as Oxycontin and Vicodin. The U.S. Government is now taking steps to reverse this epidemic, which it has blamed on easy access to prescription drugs over the Internet.

Side effects of analgesic use may include ulceration and gastric irritation (with NSAIDs), as well as reduced digestive function (a side effect of opioids).