The advocates believed they also have another win, too, in Alaska, as a legal pot measure held a steady lead.
The only major loss for drug-law reformers came in Florida and even there, a medical marijuana proposal earned 58 per cent just shy of the 60 per cent required to pass.
As Republicans swept to power in the Senate, the results emboldened marijuana activists as they prepare legalisation efforts in California, Massachusetts, Maine and other states in the next presidential election year.
Legalisation opponent Kevin Sabet called the votes "a bit of a wake-up call before 2016," noting that drug policy groups had spent millions on the legalisation campaigns, vastly outspending opponents.
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The measures were among many that appeared on ballots, with voters approving ones to raise the minimum wage in four states, passing expanded gun background checks in Washington state and rejecting abortion-related measures in two states.
The marijuana votes were considered by many to be the first real test of marijuana reform's popularity since Washington state and Colorado passed the nation's first legal pot laws in 2012, boosted then by the higher turnout among young people typical of presidential election years.
Yesterday's vote saw voters in the Washington capital district make it legal to possess up to two ounces of pot and up to three mature marijuana plants for personal use, but it does not provide for the legal sale of marijuana.