Liberal Democrat members have called for a review of drug laws including the possibility of partial decriminalisation.
Delegates attending the Lib Dem conference in Birmingham voted overwhelmingly in favour of setting up an independent panel to review the 1971 Misuse of Drugs Act.
The motion passed on Sunday afternoon said there was increasing evidence that the UK's drugs policy was "not only ineffective and not cost-effective but actually harmful, impacting particularly severely on the poor and marginalised".
And it said the the panel should consider reform of the law, based on the Portuguese model, so that possession of any controlled drug for personal use would not be a criminal offence.
Lib Dem MP Tom Brake, who sits on the party's internal home affairs committee, said there was an urgent need for "evidenced based drugs policy".
"We want to ensure the Government has a clear focus on prevention and reducing harm by investing in education, treatment and rehabilitation, and moving away from criminalising individuals and vulnerable drug users," he said.
"We need proper regulation and investment if we are to get to the root of the battle with drugs. Liberal Democrats are the only party prepared to debate these issues."