http://www.physorg.com/news106911906.html
Tramadol Hydrochloride [USA Brand name ULTRAM and ULTRACET (WITH APAP)] has been used in Europe since 1978 as a quasi-opiate pain killer. It has a very limited affinity for the mu opioid receptors, does not cause much respiratory depression, and its analgesic properties are not completely reversed by naloxone. Tramadol is a racemic mixture with one isomer (i think the +) mainly responsible for both the serotogenic profile and the desmethylated metabolite, along with the (-) isomer, which isn"t thought to contribute to the pain killing properties, but modulates the uptake of norepinephrine, which may be the reason for it"s lack of unwanted sedation. Interestingly enough, it seems the way in which it is metabolized (through the Cytochrome 450 isoenzyme) that is responsible for the extent to which desmethylation and likely other biomechanisms lead to the production of mu-opioid binding active metabolites. A very small number of individuals are theoretically predisposed to finding Tramadol "pleasurable", while recovering narcotic addicts may also find Tramadol appealing for it"s documented efficacy at making opiate withdrawals less painful.
Most people taking Tramadol as prescribed by a physician find it easy to discontinue but there is a controversy regarding it"s supposed potential for producing withdrawals of the mu-opioid type. As a patient who has taken Tramadol for 3 years due to chronic back pain, I have been fortunate enough to know about Tramadol"s pharmacology/pharmokinetics, allowing me to stay at the same dosage (it takes a long time to kick in. I"ve known people who are used to hydrocodone/demerol or NSAIDS like ibuprofen and they find the effects of tramadol to be almost unpredictable. They sometimes say it makes their pain worse, and causes agitation. That would be expected if only the (-) isomer of the racemic mixture was metabolized by their body. It is a very interesting drug, but if you are prescribed it by a MD, start very slowly and titrate upwards over a few weeks. I treat it like an antidepressant (it"s chemical structure is strikingly similiar to Venlaxafine (EFFEXOR), a well known and popular medication that belongs to a new class of antidepressants called SSNRI"s (SELECTIVE SEROTONIN AND NOREPINEPHRINE REUPTAKE INHIBITORS) which also includes Duloxetine (CYMBALTA). Taper off Tramadol as you would an antidepressant. If you are physically dependent to opiates, talk to your doctor before taking Tramadol because it may initiate intense opiate withdrawals due to it"s affinity and partial antagonistic action at the mu-opioid receptor. It also lasts about half as long as methadone as far as I know. This atypical painkiller (TRAMADOL) brand name ULTRAM has a low abuse potential, but that"s understandable due to it"s high incidence of side effects, and it"s incompatibility with most patients as a breakthrough pain med or it"s use in conjunction with other SSRI"s, Tricyclics, or MAOIS.