In a US first, the state of Oregon is set to decriminalise the possession of all drugs, including heroin, methamphetamine and cocaine.
Oregonians on Tuesday approved ballot Measure 110, according to media projections, which stops the possession of small amounts of illicit drugs from being punishable by jail time.
Instead of jail, Oregon residents will pay a small fine or can opt to attend a rehab clinic.
Meanwhile, voters in the US capital, Washington DC, and in the states of Arizona and New Jersey have backed measures to decriminalise marijuana and some psychedelic drugs.
In Washington, 77 per cent of voters are saying 'yes' to effectively decriminalising a range of psychedelic plants and mushrooms, according to the board of elections, with ballots still being counted on Tuesday.
The initiative would lower the priority for the enforcement of laws against the non-commercial possession, distribution and cultivation of such hallucinogenic substances, and ask prosecutors to drop cases related to those activities.
Arizona and New Jersey joined 11 other states in legalising recreational marijuana, according to media projections.
In New Jersey, with 49 per cent of precincts reporting, 67 per cent of voters approved a ballot measure to make cannabis legal, broadcaster NBC said. Industry experts have said it would take at least a year until adults would be able to buy the drug in the Garden State.
Montana and South Dakota were also deciding on recreational marijuana legalisation on Tuesday. Mississippi and South Dakota voted on medical marijuana measures.
The ballot initiatives were only part of the flood of choices US voters were being asked to make on Tuesday, along with their votes for the presidency, Senate and House of Representatives.
Also on the ballot were sheriffs, judges and prosecutors, and voters in 32 states decided on 120 ballot initiatives on issues ranging from tax policies to drug reforms.
Additional reporting by Evan Young and Rashida Yosufzai.
