The leftist party of Yanis Varoufakis, a former finance minister and critic of the conservative government, said he had been charged based on admitting he had tried ecstasy once.

Mr. Varoufakis, a famously outspoken left-wing economist, author and critic of Greece’s conservative government, was charged with “promoting and advertising drugs,” according to his party, known as MeRA25, or the European Realistic Disobedience Front.