The UK government has rejected a recommendation to downgrade Ecstasy pill's risk classification.
Professor David Nutt, who chairs the Advisory Council on the Misuse of Drugs, had said it was "harmful" but not damaging enough to be in class A alongside heroin and cocaine.
But the government would not buy the argument. Ministers accepted 11 of the 13 recommendations made by the council, but rejected the move to reclassify.
It also rejected the idea that drug testing kits should be given out to users to check their tablets are not contaminated.
Prof. Nutt accused ministers of being influenced by "politics" and not scientific evidence
He said: "Our job is not to give messages to the public. Our job is to tell the Home Secretary and drugs minister about the relative harms of drugs. I think they have accepted our evidence but I think they have made a political decision. There is no doubt ecstasy is harmful but it isn't as harmful as heroin or cocaine."
Prof Nutt said ecstasy had been put in class A when it was discovered because it was believed, wrongly, to be a hallucinogenic drug like LSD.
Their review is the first "systematic" examination of all the scientific evidence about the impact of taking the drug, he said.
"Government is about politics and I guess, in an ideal world, the two would be harmonious and synchronised but in a way that's a question you should be asking the politicians."
Prof Nutt has faced criticism after claiming in an academic journal that taking ecstasy is no more dangerous than horse riding.
Prime Minister Gordon Brown's spokesman told reporters: "As the Home Office have been making clear, the Government firmly believes that ecstasy should remain a class A drug."
Asked what purpose the Advisory Committee served if the Government did not accept its recommendations, the spokesman said: "The Home Office has not requested the Advisory Committee on the Misuse of Drugs to review the classification of ecstasy. It is doing it at the request of the (Commons) Science and Technology Committee.
"They make recommendations but it is ultimately for the Government to make decisions and set policy and it is our view that ecstasy should remain a class A drug."