The Answer:

The most common drug is actually a combination of sodium pentothal, pavulon and potassium chloride.

The sodium pentothal slackens the muscles, depresses the central nervous system and induces unconsciousness. The pavulon blocks the exchanges between nerves and muscles, suppressing the respiratory system and beginning to stop the heart. And finally, the potassium chloride stuns the heart to stop it altogether with an electrolyte imbalance.

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