Types of Opioids
There are many different types of opioids that are used medicinally. Although the term opiate is often used to refer to opioids as well, the term opiate technically refers to only the alkaloids that occur naturally in opium, the resin of the opium poppy (Papaver Somniferum). The semi-synthetic substances that are directly derived from the opium poppy are also sometimes grouped in the term 'opiates' as well, while other times these substances are simply referred to as semi-synthetic opioids. On this website, you may come across instances where both natural opiates and synthetic and semi-synthetic opioids are referred to simply as opioids, and other instances where a distinction is made between between naturally occurring opiates and semi-synthetic and fully-synthetic opioids.
There are a number of classes of opioids. Three of these classes, natural opiates, semi-synthetic opioids, and synthetic opioids are commonly referred to as narcotic, or painkilling opioid drugs. The naturally occurring opiates are those which are found in the opium resin of the opium poppy. Although there are over 25 different alkaloids present in opium, morphine and codeine are the only two that are used as narcotic opiate analgesics. All other opioid analgesic medications are either semi- or fully-synthetic and are not found in nature. The semi-synthetic opioids such as hydrocodone, hydromorphone, oxycodone, and oxymorphone are derived from the naturally occurring opiates and opium alkaloids (morphine and thebaine especially). Fully-synthetic opioids such as methadone and fentanyl are synthesized from other chemicals and molecules that do not come from alkaloids found in opium.
There are other classes of opioids as well, including the endogenous opioids. These are peptides that are produced naturally in the body, such as endorphins, enkephalins, dynorphins, and endomorphins. Endorphins get their name from "endogenous morphine", meaning "morphine produced naturally in the body." There are also drugs such as tramadol and tapentadol that are chemically not of the opioid class, but do have agonist actions at the μ-opioid receptor.
Click on a link below to get more details regarding a certain opiate/opioid. The same links can also be found in the navigation column on the left side of the website.
- Schumacher MA, Basbaum AI, Way WL, Opioid Analgesics & Antagonists (Chapter 31) in: Basic and Clinical Pharmacology. 12e. Katzung BG, Masters SB, Trevor AJ (Editors). (McGraw-Hill / Lange, 2012)
- Holden JE, Jeong Y, Forrest JM. The endogenous opioid system and clinical pain management. AACN Clinical Issues Jul-Sep 2005; 16(3):291-301. [PubMed]