Editing Narcotic (section)

==Analgesics==
[[Analgesics]] are drugs that relieve [[pain]]. There are two main types: non-narcotic analgesics for mild pain, and narcotic analgesics for severe pain.<ref>[https://www.fda.gov/Drugs/DevelopmentApprovalProcess/HowDrugsareDevelopedandApproved/ApprovalApplications/InvestigationalNewDrugINDApplication/ucm176533.htm General Drug Categories]. Fda.gov (2009-08-11). Retrieved on 2011-09-24.</ref>

===Narcotic analgesics===
Narcotic analgesics tend to be [[opioid]]s. They bind to [[opioid receptor]]s which are [[G protein-coupled receptor|G protein-coupled receptors]] distributed in brain, spinal cord, digestive tract, peripheral neurons.<ref>{{cite journal|pmid=8981566|year=1996|last1=Dhawan|first1=B. N.|last2=Cesselin|first2=F.|last3=Raghubir|first3=R.|last4=Reisine|first4=T.|last5=Bradley|first5=P. B.|last6=Portoghese|first6=P. S.|last7=Hamon|first7=M.|title=International Union of Pharmacology. XII. Classification of opioid receptors|journal=Pharmacological Reviews|volume=48|issue=4|pages=567–92}}</ref>

====Mechanism====
There are three types of opioid receptors: mu ([[μ-opioid receptors]]), delta, and kappa ([[κ-opioid receptor]]). Endogenous opioids ([[enkephalins]], [[dynorphin]], [[endorphin]]) do not bind specifically to any particular opioid receptor. Receptor binding of the opioid causes a cascade leading to the channel opening and [[Hyperpolarization (biology)|hyperpolarization]] of the neuron. The opioid receptors have the following channel types: mu, K<sup>+</sup> channel; l delta, K<sup>+</sup> channel; kappa, Ca<sup>2+</sup> channel. Hyperpolarization can lead to post-synaptic neural inhibition and presynaptic inhibition of neurotransmitter release. Post-synaptic neural inhibition can reduce analgesia and central hyperactivity may reduce its efficacy. The mechanism of kappa receptors is slightly different from mu and delta, in that Ca<sup>2+</sup> channels close instead of K<sup>+</sup> channels, and K<sup>+</sup> channels open in mu and delta.<ref name="Dickenson1991">{{cite journal|last1=Dickenson|first1=A H|title=Mechanisms of the analgesic actions of opiates and opioids|journal=British Medical Bulletin|volume=47|issue=3|year=1991|pages=690–702|issn=1471-8391|doi=10.1093/oxfordjournals.bmb.a072501|pmid=1665377}}</ref>