What is the differace between Tramadol HCL and Hydrocodone?

Hydrocodone & tramadol are both opioid agonist analgesics. They are both micro (morphine) agonists, and (unlike buprenorphine), they are both full agonists, and not partial. Although tramadol's chemical structure is simpler than that of hydrocodone, its pharmacology is more complex. And even though their pharmacologies differ, somewhat, both share key features related to the prototype narcotic, codeine. Both tramadol and hydrocodone share a 3-methyl ether grouping (as does codeine), and all three are demethylated by the liver to corresponding, more active phenols. Although tramadol is arguably a less potent analgesic than hydrocodone, it is difficult to compare and contrast the relative ratio equivalencies between the two, because hydrocodone's absolute potency equivalency has not been established. In other Words, unlike many other narcotics, experts do not agree on how potent and efficacious hydrocodone really is. Most believe hydrocodone is less potent than oxycodone, but the extent of the reduced potency here is debatable (the relative differences in potency between the analogous hydromorphone vs oxymorphone (Dilaudid vs Numorphan), is more straight forward. Tramadol has significant SNRI action, while hydrocodone does not. Interestingly, however, both hydrocodone and codeine can cause seizures, but not as readily as tramadol (or pethidine, for that matter). There is some evidence that hydrocodone, along with codeine and oxycodone, might have very mild SNRI effects, just as tramadol does, but much weaker. Tramadol itself is a very weak opioid agonist, and most of the opioid agonist effect derived from the compound is through a hepatic demethylation. However, unmetabolized tramadol has a rewarding effect (dopamine, rat, NAC shell) clearly in greater potency than is accountable by its very weak mU opioid effect. Could it be that unmetabolized (parent) tramadol behaves similarly to the drug MDMA, and that the metabolised M1 is similar to hydrocodone? Now, a portion of the human population can not effectively perform 3 ortho demethylation, and these people probably will derive lesser analgesic benefit from tramadol, codeine, and even hydrocodone and oxycodone, and in this rank ordering of significance. Tramadol is a synthetic analog of codeine. Hydrocodone is a conger of codeine, as is oxycodone. Phenomenologically, it is best to think of tramadol as a weak version of ketobemidone, for those in which the drug is efficacious. Both analgesics raise the seizure threshold, and both are nmda-antagonists. The specific "leg pleasure" both drugs produce, coupled with not wanting to move one's body whatsoever, is a striking similarity. It would appear, perhaps, that not only does tramadol have far greater abuse potential than previously thought, but that, in fact, tramadol may represent one of the most abusable of all opioids, and even greater than heroin.