Aconitine - Numbs the pain, then breaks your heart

So yeah, aconitine is basically the annoying emo version of an alkaloid. Or something like that.

If one was so inclined as to do a fancy chemical extraction from the mashed up vegetative matter of any plant belonging to the genus Aconitum (otherwise known as aconite, monkshood, soldier's cap, helmet flower, or wolfsbane), one might be able to isolate a chemical called aconitine (along with a number of very similar alkaloids) capable of acting as both an analgesic (painkiller) and a cardiotoxin (causes arrhythmias, which are basically when your heartbeat gets thrown out of whack). Incidentally, the hood/cap/helmet name is the result of the characteristic helmet-shaped flowers that species of Aconitum produce. Also, wolfsbane sounds awesome (see also, the seemingly way less intimidating yet also very poisonous henbane).

Extracts of Aconitum species are used in traditional Chinese medicine to treat pain and inflammation. This is a great example of how natural/herbal remedies are often more dangerous than the drugs they attempt to replace. There's a damn good reason that aconitine has never caught on as a painkiller, and yet has occasionally been used to poison people.

Aconitine is thought to bind to and open voltage-dependent sodium channels in the heart and central nervous system, resulting in the disruption of electrical conduction in the heart (producing arrhythmias) and pain signals to the brain (producing analgesia) [1]. Because it has this particular mechanism of action, it is used to create animal models of cardiac arrhythmia, which help researchers to develop new antiarrhythmic agents [1].

[1] Gutser UT et al. (1998). Mode of antinociceptive and toxic action of alkaloids of Aconitum spec.. Naunyn Schmiedebergs Arch Pharmacol 357: 39-48.