Tetrodotoxin is a very effective nerve toxin inducing rapid, profound paralysis. It is the poison which makes puffer fish so dangerous to eat. The first symptom of intoxication by this poison is a slight numbness of the lips and tongue, appearing between 20 minutes to three hours after eating poisonous pufferfish. The next symptom is increasing paraesthesia (paralysis in laymans terms) in the face and extremities, which may be followed by sensations of lightness or floating. Headache, epigastric (read stomache ache) pain, nausea, diarrhea, and/or vomiting may occur. Occasionally, some reeling or difficulty in walking may occur. The second stage of the intoxication is increasing paralysis. Many victims are unable to move; even sitting may be difficult. There is increasing respiratory distress (it gets harder to breath). Speech is affected, and the victim usually exhibits dyspnea, cyanosis, and hypotension. Paralysis increases and convulsions, mental impairment, and cardiac arrhythmia may occur. The victim, although completely paralyzed, may be conscious and in some cases completely lucid until shortly before death. Death usually occurs within 4 to 6 hours, with a known range of about 20 minutes to 8 hours.
This and a toxin excreted form the glands of the Bufo marinus (a poisinous cane toad) help to create the initial death of a zombie.(I have been unable to find a name of any kind for the toxin, and its specific quaities also seem to be eluding me). The mixture of the toxin and the potent hullucinogenic anesthenic qualites of the excretion help to induce what seems to be death but is in truth a paralysis of all limbs and a slowing of the heart and other bodily functions that appears to be death. One can assume that by combining the toxin and the excretion that the inevitable death that the tetrodotoxin would cause without an antidote is staved off and the effects that occur before death are extended indefintely till starvation of body or air occurs.
Administer this with the other drug Datura, one derived from the aptly named zombie cucumber or Datura stramonium (a large, white, trumpet-shaped flower which blooms March through November. Corollas are up to 6 inches long, have 5 teeth and are often tinged with purple or lavender around the margins. This foul-smelling flower opens after dusk and closes by mid-morning of the following day.) help to create an easily controlled, nearly mindless zombie slave.
The effects of the Datura include delusions, mental confusion, disorientation, amnesia. If this dangerous drug is taken in large enough doses it can put one into an impenatrable stupor. 
Datura has long been used by native peoples of the Southwest in puberty and other ceremonies because of the plant's halucinogenic alkaloids. People trying to imitate Native American ways have often poisoned themselves, sometimes fatally.
