White, odorless, bitter, crystalline powder.
Tramadol is a pain reliever (analgesic). It's action is similar to opioid narcotics such as codeine and morphine, but it does not depress breathing like they can, and is less prone to abuse and addiction.
Tramadol is an alkaloid, with an amine group (where the nitrogen atom is), which puts it in a group of bitter plant chemicals that often have potent biological activity.
Alkaloids range from the Belladona alkaloids like atropine and scopalomine that are used as poisons, cold remedies, and truth serums, to dextromethorphan, a cough suppressant (anti-tussive).
But the most widely known alkaloids are the opiates, such as morphine, heroin, fentanyl, oxycodone, and methadone. These act on receptors in the brain that are normally activated by small proteins (peptides) called endomorphins or endorphins.