Chemicals in medicines – analgesics

Any drug that relieves pain selectively without blocking the conduction of nerve impulses, markedly altering sensory perception, or affecting consciousness. This selectivity is an important distinction between an analgesic and an anesthetic.

Analgesics are those drugs that mainly provide pain relief. The primary classes of analgesics are the narcotics,including additional agents that are chemically based on the morphine molecule but have minimal abuse potential;nonsteroidal anti-inflammatory drugs (NSAIDs) including the salicylates; and acetaminophen. Other drugs, notablythe tricyclic antidepressants and anti-epileptic agents such as gabapentin, have been used to relieve pain, particularlyneurologic pain, but are not routinely classified as analgesics.


Pain has been classified as "productive" pain and "non-productive" pain. While this distinction has no physiologicmeaning, it may serve as a guide to treatment. "Productive" pain has been described as a warning of injury, and so maybe both an indication of need for treatment and a guide to diagnosis. "Nonproductive" pain by definition serves nopurpose either as a warning or diagnostic tool.

Traditionally, pain has been divided into two classes, acute and chronic, although severity and projectedpatient survival are other factors that must be considered in drug selection.

Acute pain

Acute pain is self limiting in duration, and includes post-operative pain, pain of injury, and childbirth. Because pain ofthese types is expected to be short term, the long-term side effects of analgesic therapy may routinely be ignored. Thus,these patients may safely be treated with narcotic analgesics without concern about possible addiction, or NSAIDs withonly limited concern for the risk of ulcers.

Chronic pain

Chronic pain, pain lasting over three months and severe enough to impair function, is more difficult to treat, since theanticipated side effects of the analgesics are more difficult to manage. In the case of narcotic analgesics this means theaddiction potential, as well as respiratory depression and constipation. For the NSAIDs, the risk of gastric ulcers limitdose.