America's dependence on such imports stems from a shortage of sodium thiopental, part of the three-drug cocktail used in most executions.

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Sodium thiopental, an anaesthetic, is used in a massive dose to induce a coma in condemned prisoners, before two other drugs are used to kill them.

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Sodium pentothal, the trade name for thiopental, is the best-known of a class of barbiturates popularly supposed to act as truth serums.

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