An independent panel should consider legalising cannabis as part of a wide-ranging review of drug laws, the Liberal Democrats said.
The experts should also consider whether possession of any currently illegal drug should remain a criminal offence.
The motion was passed by the Liberal Democrat conference in Birmingham as a senior lawyer told activists that current drug policy is not working.
Alistair Webster QC, a crown court recorder and chairman of the Lib Dem lawyers association, told the conference: "I have practised in the courts, both as an advocate and judge, for over 30 years and it's plain to anybody who has spent time in that way that the drug policy which we have followed since 1967 is not working."
He acknowledged that "decriminalisation, per se, carries with it its own problems" but said the motion called for an "intelligent reassessment - start again, look again and see where we can get it better".
Ewan Hoyle, from South Glasgow, proposed the policy and told the conference that politicians had not tackled the issue because of "cowardice" in the face of a potentially hostile backlash in the press.
He said: "The war on drugs is not working, but it's essential that we keep fighting. Drugs are harmful, they can take young people to places that are every parent's worst nightmare: insanity, disease, destitution, prostitution, death.
"We have to keep fighting in the best way we can to stop young people from all walks slipping into lives of misery and early graves.
"But we are still fighting a massive 21st century drug problem with 20th century methods."
The motion calls for a panel to review the 1971 Misuse of Drugs Act and consider reforms of the law so that "possession of any controlled drug for personal use would not be a criminal offence".
The experts would consider whether possession would be "prohibited" but "should cause police officers to issue citations" for users to appear before panels who would determine whether health, education or social interventions were necessary.
As an alternative, the panel would also consider "potential frameworks for a strictly controlled and regulated cannabis market".
Mr Hoyle called for cannabis to be sold in chemist shops where it could be regulated.
He said: "The motion calls for models of cannabis regulation to be investigated. I personally favour sale from pharmacies.
"If we want to send a message that cannabis is harmful - and we should - how better to do so than through a health professional at the point of intended purchase?
"No pharmacist is going to suggest the customer progresses to the use of heroin or crack. And no pharmacist would sell to a child."
Mr Hoyle said in Portugal and Switzerland they had followed expert advice to treat drug use as a medical rather than a moral or criminal issue.
But in the UK there was no political will to change the system, which resulted in a £6 billion illegal drug market.
He said: "It isn't taxed and the vast majority of the profits go into the hands of organised criminal gangs. This includes millions of pounds to the Taliban in Afghanistan, with which they can purchase the bombs and bullets that murder our brave soldiers.
"We have to stop enriching our criminals."
The drug trade had created "criminal idols" - drug dealers who are looked up to as role models and employers in deprived areas.
"We could undermine these criminal idols if we removed their control of the drug trade and placed it in to the careful hands of the state", he said.
Activist Adam Corlett accused politicians of double standards over drugs policy.
He said: "Many MPs and even ministers seem to be more averse to drugs policy than to drugs themselves."
Duncan Scott, from the Oxford East Lib Dems said: "There's a hypocrisy in our drug laws. Culturally, our attitude towards drug use just doesn't merit our attitude towards other forms of illegal behaviour."
George Miles told the conference: "Taxation of cannabis could net £2 billion a year, says one estimate, which would build hospitals instead of funding terrorists."
He added: "John Lennon and Eric Clapton didn't say legalise heroin or cocaine, but Bob Marley says legalise cannabis."
But Councillor Julian Cooper, from Witney, spoke against the potential legalisation of cannabis.
He said: "I think there's a misconception in this that legalisation would solve a lot of those problems."