Tramadol

Tramadol hydrochloride (Ultram, Tramal others below) is a centrally acting opioid analgesic, used in treating moderate to severe pain. The drug has a wide range of applications, including treatment for restless leg syndrome, acid reflux, andfibromyalgia. It was developed by the pharmaceutical company Grünenthal GmbH in the late 1970s.

Tramadol possesses weak agonist actions at the μ-opioid receptor, releases serotonin, and inhibits the reuptake of norepinephrine

Tramadol is a synthetic analog of the phenanthrene alkaloid codeine and, as such, is an opioid and also a prodrug (codeine is metabolized to morphine, tramadol is converted to O-desmethyltramadol). Opioids are chemical compounds which act upon one or more of the human opiate receptors. The euphoria and respiratory depression are mainly caused by the μ₁ and μ₂ receptors; the addictive nature of the drug is due to these effects as well as its serotonergic/noradrenergic effects. The opioid agonistic effect of tramadol and its major metabolite(s) are almost exclusively mediated by the substance's action at the μ-opioid receptor. This characteristic distinguishes tramadol from many other substances (including morphine) of the opioid drug class, which generally do not possess tramadol's degree of subtype selectivity

Source ; Wikipedia