For the first time more Australians support decriminalising the use of marijuana than those who back retaining its classification as an illicit drug, a survey conducted over three decades has found.

There has been a significant shift in sentiment around marijuana use since 2013, research has found, with experts pinpointing two critical factors: the legalisation push sweeping the United States and official acceptance by federal and state governments that cannabis has a part to play in pain relief for sufferers of disease.

The Australian National University's 30-year election study found a sharp switch from 2013 when 44 per cent of those surveyed said the use of marijuana should remain a criminal offence compared to 34 per cent who supported legalisation and the remainder, 22 per cent, undecided.

By 2016, that had flipped to 43 per cent backing legalisation and just 32 per cent support for the criminal status quo.