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.
After examining a range of approaches, from zero-tolerance to decriminalisation, it concluded drug use was influenced by factors "more complex and nuanced than legislation and enforcement alone".
But it found there had been a "considerable" improvement in the health of drug users in Portugal since the country made drug possession a health issue rather than a criminal one in 2001.
The Home Office said these outcomes could not be attributed to decriminalisation alone.
But Mr Baker believes treating drug use as a health matter would be more effective, "rather than presuming locking people up is the answer".
Back in the 1990s Portugal was struggling with a heroin epidemic of almost epic proportions. One person in every 100 was a heroin addict.
Not everyone agreed with the approach that was adopted to try and end the problem. In fact, many on the right wing of politics were appalled when prosecutions for people using drugs were ended.
They didn't like the idea that addiction would be treated as a health issue, rather than a criminal one, that addicts would be given treatment and healthcare to help them overcome their addiction. Those voices have been silenced now.
Fifteen years later, and the number of people hooked on heroin has been halved, and there have been good results in terms of Aids infection, hepatitis infection and the like.
Back in the 1990s "we feared that Portugal could turn into a paradise for drug users", says Dr Jaoa Goulao, Portugal's national co-ordinator on drugs and drug addiction.
Thanks to the policy, that didn't happen, he says.
Drugs 101
Drugs 101
“If you trust in yourself, and believe in your dreams, and follow your star. . . you'll still get beaten by people who spent their time working hard and learning things and weren't so lazy.”