A drug that reduces pain (pain reliever = analgesic) without reducing consciousness. There are three main categories of analgesic :

1. Opioid Analgesics . Chemically related to morphine, a substance extracted from poppies. Very effective in relieving pain but have many side effects. These include: tolerance ; risk of withdrawal symptoms; constipation; sleepiness; nausea. Overdose results in coma and eventually death.

2. Nonopioid Analgesics . All of this class of analgesics, except acetaminophen, are NSAIDs . These drugs work by interfering with the system responsible for pain - the prostaglandin system - as well as reducing inflammation and irritation around a wound. Aspirin is the classic example of this class of drugs. NSAIDs have the side effects of causing peptic ulcers and stomach irritation.

3. Adjuvant Analgesics . Usually given for reasons other than pain relief, but may relieve pain in certain circumstances. For example, some antidepressants are also nonspecific pain relievers and are used to treat chronic pain such as lower back pain and headaches.