That means they will have to consider alternative policies at home, even at decriminalisation.
However, it does not call for the decriminalisation or legalisation of most drugs.
The Home Office is undertaking an international study on "alternative approaches" used in other countries, including some forms of decriminalisation.
Even after the decriminalisation of homosexuality, he remained fairly discreet in public.
Two former home secretaries, Liberal Democrat Lord Jenkins of Hillhead and the Tory, Lord Baker of Dorking, told the Sunday Times they favoured decriminalisation.
"The Obama administration has been quite clear in our opposition to the decriminalisation or legalisation of illicit drugs, " Mr Restrepo was quoted as saying by the Associated Press.
He did not refer to a recent proposal by Guatemalan President Otto Perez Molina that the decriminalisation of drugs should be considered so the trade could be better controlled.
Guatemalan President Otto Perez Molina, a retired army general, has ordered his nation's army to join the fight against the trafficking gangs but also called for the possible decriminalisation of drugs.
The US remains opposed to decriminalisation, US officials say.
Prof Nutt is due to give evidence in June to the Home Affairs Select Committee, which is conducting a wide-ranging inquiry into the effectiveness of Britain's drugs policy including the arguments for decriminalisation.
In its wide-ranging report, the cross-party home affairs committee said MPs had visited Portugal as part of attempts to understand different systems of decriminalisation which were being used around the world to manage the harm of drugs, rather than just hand out penalties for their use.
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