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.