Drug that produces analgesia (see analgesic), narcosis (stupor or sleep), and drug addiction. In most people narcotics also produce euphoria. Those that occur naturally in the opium poppy, notably morphine, have been used since ancient Greek times. The main therapeutic use of narcotics is for pain relief. Most countries limit the production, sale, and use of narcotics because of their addictive properties and detrimental effects and the incidence of drug abuse. With the development in the 19th century of the hypodermic needle and of heroin, five to 10 times as potent as morphine, the use and abuse of narcotics increased dramatically. A narcotic overdose can cause central nervous system depression, respiratory failure, and death.
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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 narcotics; 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 NSAIDs (including aspirin and ibuprofen) and acetaminophen; all act by inhibiting synthesis of prostaglandins, molecules involved in the peripheral perception of pain.
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In choosing analgesia, 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 choice of analgesia is also determined by the type of pain: for neuropathic pain, traditional analgesia is less effective, and there is often benefit from classes of drugs that are not normally considered analgesics, such as tricyclic antidepressants and anticonvulsants.
The exact mechanism of action of paracetamol/acetaminophen is uncertain, but it appears to be acting centrally. Aspirin and the other non-steroidal anti-inflammatory drugs (NSAIDs) inhibit cyclooxygenases, leading to a decrease in prostaglandin production. This reduces pain and also inflammation (in contrast to paracetamol and the opioids).
Paracetamol has few side effects and is regarded as very safe, although excessive doses can lead to kidney and liver damage in the form of analgesic nephropathy and paracetamol hepatotoxicity, respectively. NSAIDs predispose to peptic ulcers, renal failure, allergic reactions, and occasionally hearing loss, and they can increase the risk of hemorrhage by affecting platelet function. The use of aspirin in children under 16 suffering from viral illness may contribute to Reye syndrome.
Opioids, while very effective analgesics, may have some unpleasant side-effects. Up to 1 in 3 patients starting morphine may experience nausea and vomiting (generally relieved by a short course of antiemetics). Pruritus (itching) may require switching to a different opioid. Constipation occurs in almost all patients on opioids, and laxatives (lactulose, macrogol-containing or co-danthramer) are typically co-prescribed.
When used appropriately, opioids and similar narcotic analgesics are otherwise safe and effective, however risks such as addiction and the body becoming used to the drug (tolerance) can occur. The effect of tolerance means that drug dosing may have to be increased if it is for a chronic disease this is where the no ceiling limit of the drug comes into play. However what must be remembered is although there is no upper limit there is a still a toxic dose even if the body has become used to lower doses.
The use of paracetamol, as well as aspirin, ibuprofen, naproxen, and other NSAIDS concurrently with weak to mid-range opiates (up to about the hydrocodone level) has been shown to have beneficial synergistic effects by combatting pain at multiple sites of action—NSAIDs reduce inflammation which, in some cases, is the cause of the pain itself while opiates dull the perception of pain—thus, in cases of mild to moderate pain caused in part by inflammation, it is generally recommended that the two be prescribed together.
The use of adjuvant analgesics is an important and growing part of the pain-control field and new discoveries are made practically every year. Many of these drugs combat the side effects of opioid analgesics, an added bonus. For example, antihistamines including orphenadrine combat the release of histamine caused by many opioids, methylphenidate, caffeine, ephedrine, dextroamphetamine, and cocaine work against heavy sedation and may elevate mood in distressed patients as do the antidepressants. A well-accepted benefit of THC to chronic pain patients on opioids is its superior anti-nauseant action. Some think it would make more sense to use the synthetic THC capsule (trade name Marinol), which is administered orally. However, in patients suffering from nausea, the swallowing of the capsule itself may provoke vomiting. Likewise, the use of medicinal cannabis remains a debated issue.