There are many drugs found in nature that are thought of as useful biological research tools to discover how the channels in neurons function.

1. Tetrodotoxin is found in pufferfish (fugu) and newts. This drug prevents sodium channel activation and the propagation of nerve impulses in neurons causing paralysis and death. The victim is often conscious until death occurs. This drug is 10,000 more times more lethal than cyanide. If a fugu pufferfish, a delicacy in Japan, is not properly prepared the guest will not live to tell the tale. Death usually occurs within 4 to 5 hours with a range of about 20 minutes to 8 hours. There is no antidote for this poison.

For voodoo enthusiasts, this toxin is said to be the main ingredient used in voodoo powder by the zombie master to zombify people.  :tongue:  If you are a zombie or want more information, you may want to check out this article on medicine zombies, they exist.

This article says that on  a beautiful spring day a stranger arrived in a market place in Haiti. He had a heavy gate and vacant eyes. The stranger said his name was Clairvius Narcisse and it was discovered that tetrodotoxin was used in zombie powder to turn into a zombie laborer on a plantation.

2. Histrionicotoxin is a toxin found in snails and frogs and also prevents sodium channel activation in neurons.

3. Batrachotoxin prevent the activation of potassium channels leading to persistent depolarization in the neuron. This toxin is found in blow dart frogs. Nerve signal transmission to the muscles is blocked.

4. Procaine and cocaine are anesthetics (produce a local or general loss of sensation including pain) that prevent sodium channel activation in neurons.  

5. Charybdotoxin (CTX) prevents sodium inactivation in neurons leading to persistent depolarization in the neuron and no nerve signal transmission. Animals with this toxin in nature include sea anemones and the African scorpion .