MONTEVIDEO, Uruguay—Uruguay moved closer to becoming the first country in the Americas to fully legalize marijuana on Wednesday, after the lower house voted to regulate the market for pot with a view to deprive drug traffickers of a key source of revenue.

The bill was approved with 50 of the 96 lawmakers present voting in favor late Wednesday after more than 12 hours of debate. The Senate, in which the ruling Frente Amplio leftist coalition has a majority, is expected to approve the measure in August.

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