Tramadol (US brand name: Ultram) is an opioid-like pain reliever and an anti-inflammatory drug. It's commonly prescribed for back pain, sprains, and arthritis, and to people who need pharmalogical pain relief but for whatever reason can't take stronger opioids like Vicodin or Percocet. It's frequently used in 30cc doses in emergency rooms as an immediate but non-euphoric (and therefore, outpatient-compatible) painkiller.
Tramadol hydrochloride (Ultram in the United States and Canada, Adolonta in Europe) is a centrally acting anti-inflamatory analgesic. The chemical name for tramadol hydrochloride is (±)cis-2- (dimethylamino)methyl-1-(3-methoxyphenyl) cyclohexanol hydrochloride. The molecular weight of tramadol hydrochloride is 299.8.
The unencapsulated drug itself is a white, bitter, crystalline and odorless powder. It is readily soluble in water and in ethanol and has a pKa of 9.41. The water/n-octanol partition coefficient is 1.35 at pH 7.
The tablets are available in 50mg, 100mg, 150mg or 200mg varieties and will be either a yellow and green gelatin tablet or a white oval tablet. Inactive ingredients in the tablet are corn starch, hydroxypropyl methylcellulose, lactose, magnesium stearate, microcrystalline cellulose, polyethylene glycol, polysorbate 80, sodium starch glycolate, titanium dioxide and wax. Tramadol comes in two forms: regular and sustained release.
Tramadol has a moderate potential for abuse (although, compared to almost all other opioids, it's pretty weak), as its effects are similar to, though not nearly as intense as, lesser opioids, like dextropropoxyphene. Taking 150mg to 350mg (with 400mg being the dose where problems begin to occur—i.e., the necessity of a charcoal milkshake) produces roughly the same effect as about 10mg of codeine, only without an opioid's more unpleasant side effects (itching, vomiting, loss of alertness). In moderate to high doses, tramadol produces slight dizziness, extremely mild, almost unnoticeable euphoria, and mild stomach upset. In very high doses (>400mg), severe stomach upset, unpleasant hallucinations and seizures can occur.
Tramadol was not an FDA-scheduled drug in the United States for much of its early existence, despite its potentially addictive properties. It's the only opioid that isn't Schedule I or II. In 2003, it was moved to Schedule IV.
It has been noted that tramadol eases the comedown of several recreational drugs, notably MDMA and LSD, although I suspect that this is purely conjecture, as I've done both of those drugs and I've gone through courses of tramadol for pain, and I can't imagine it doing much for calming people down, at least not as well as any benzodiazepine or hypnotic sedative.
Sources:
http://www.rxlist.com/cgi/generic/tramadol.htm