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 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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Most recently, the Indian government is reported to have administered thiopental last June to seven Muslims suspected of causing the Gujarat train fire.

ECONOMIST: Drugs cannot make you tell the truth

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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James Cottrell, the president of the American Society of Anaesthesiologists, says that although thiopental sometimes makes people talk more, it does nothing to ensure that what they say is truthful.

ECONOMIST: Drugs cannot make you tell the truth

Dr Cottrell does not believe that thiopental has any long-term adverse affects, though Vincent Iacopino, acting director of research for Physicians for Human Rights, an American charity, cautions that it can be addictive.

ECONOMIST: Drugs cannot make you tell the truth