There is "no obvious" link between tough laws and levels of illegal drug use, a government report has found.
Liberal Democrat Home Office minister Norman Baker said the report, comparing the UK with other countries, should end "mindless rhetoric" on drugs policy.
He accused the Conservatives of "suppressing" the findings for months.
Prime Minister David Cameron said the research did not offer "specific conclusions" and said he did not "believe in" decriminalising drugs.
Drugs policy was debated in the House of Commons earlier, with Green MP Caroline Lucas urging the government to review "failing" drugs laws.
Under current laws, offenders can be jailed for up to seven years for possessing Class A drugs, and can be jailed for life for producing or supplying drugs.
The Home Office report compared the UK's approach to drug misuse with that of 13 other countries.