Some MPs want decriminalisation of drugs
They said ministers should focus attention on prevention and helping addicts instead of prohibition.
Home Secretary David Blunkett's recent request for a review of arguments for reclassifying cannabis also roused MPs in Friday's Commons debate.
He said that unless more effective messages got through to young people about drugs, the number of addicts, crimes caused by drugs and lives destroyed would rise.
Labour MP Jon Owen Jones, who is piloting a backbench Bill aimed at legalising cannabis, said: "On an evidence base ... the policies that have been carried out to date are not working."
Paul Flynn, also for Labour, asked the minister for examples of "any anti-legal or illegal drugs education in the UK or anywhere else, which has achieved a reduction in drug use".
Simon Hughes, for the Liberal Democrats, described the government's drugs policies as "a total failure".
He said: "We have had some of the harshest penalties for drugs use in Europe and yet drugs use has increased more and is at a higher level than almost anywhere else in Europe."
Other countries are increasingly decriminalising, he added
Mr Ainsworth rejected Mr Hughes' comments, saying that despite good work being done in the UK changes took time to be realised.
He maintained that there was no need to decriminalise drugs to focus on prevention.
Reclassifying cannabis
There was evidence proving that treatment was working, he said, particularly in prisons.
He also pointed to advances being made by drug education programmes in schools.
David Blunkett has asked for a review of arguments for reclassifying cannabis from class B to C under the Misuse of Drugs Act.
Mr Hawkins said the home secretary had to "justify by evidence" such a major change in the law.
"We hope the government will stick to what the minister said at the outset, that all drugs are dangerous, that all drugs should remain illegal ... ".
Mr Ainsworth said reclassifying cannabis as a class C drug would keep it controlled and said using it would still be a criminal offence.
'Credibility enhanced'
"But if reclassification is warranted by an honest scientific assessment of the relative harms this will enhance the credibility of our drug laws as a whole and help us to deliver our message on drugs to young people and better align public policy with criminal justice practice," he said.
A decision on possible reclassification next spring would follow the home secretary's announcement, MPs were told.
Mr Ainsworth said Afghanistan was the largest single supplier of heroin - producing 90% of the drug available in the UK.