Physical pain is the unpleasant feeling common to a headache and a stubbed toe. It typically consists of unpleasantness and motivation to withdraw and protect, and has location, duration, intensity and a distinctive quality (e.g., burning, stabbing). Pain is often accompanied by other bodily feelings (e.g., nausea, fatigue), negative emotions (e.g., fear, anxiety, anger, irritability), and cognitive impairment (e.g., attention and working memory deficits).

For scientific and clinical purposes, pain is defined by the International Association for the Study of Pain (IASP) as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage". A definition by Margo McCaffery, widely used in nursing since 1968, reflects pain's subjective nature: "Pain is whatever the experiencing person says it is, existing whenever he says it does".

Pain is part of the body's defense system, triggering a reflex reaction to retract from a painful stimulus, and helps adjust behavior to increase avoidance of that particular harmful situation in the future. Physical pain is linked to various cultural, religious, philosophical and social issues.

Types of pain

Acute pain, such pain resulting from trauma, often has a reversible cause and may require only transient measures and correction of the underlying problem. In contrast, chronic pain often results from conditions that are difficult to diagnose and treat, and that may take a long time to reverse. Some examples include cancer, neuropathy, and referred pain. Often, pain pathways (nociceptors) are set up that continue to transmit the sensation of pain even though the underlying condition or injury that originally caused pain has been healed. In such situations, the pain itself is frequently managed separately from the underlying condition of which it is a symptom, or the goal of treatment is to manage the pain with no treatment of any underlying condition (e.g. if the underlying condition has resolved or if no identifiable source of the pain can be found).

Analgesic

An analgesic (also known as a painkiller) is any member of the diverse group of drugs used to relieve pain (achieve analgesia). The word analgesic derives from Greek an- ("without") and algos ("pain"). Analgesic drugs act in various ways on the peripheral and central nervous systems; they include paracetamol (para-acetylaminophenol, also known in the US as acetaminophen), the non-steroidal anti-inflammatory drugs (NSAIDs) such as the salicylates, narcotic drugs such as morphine, synthetic drugs with narcotic properties such as tramadol, and various others.

In choosing analgesics, the severity and response to other medication determines the choice of agent; the WHO pain ladder, originally developed in cancer-related pain, is widely applied to find suitable drugs in a stepwise manner. The analgesic choice is also determined by the type of pain: for neuropathic pain, traditional analgesics are less effective, and there is often benefit from classes of drugs that are not normally considered analgesics, such as tricyclic antidepressants and anticonvulsants.