Jeff Sessions, the US Attorney General, has described marijuana as “only slightly less awful” than heroin.
The man Donald Trump selected to be the Government's chief lawyer outlined his stance on drug use in a speech to police chiefs on Wednesday.
“I realise this may be an unfashionable belief in a time of growing tolerance of drug use,” he said, “but too many lives are at stake to worry about being fashionable.
“I reject the idea that America will be a better place if marijuana is sold in every corner store. And I am astonished to hear people suggest that we can solve our heroin crisis by legalising marijuana – so people can trade one life-wrecking dependency for another that’s only slightly less awful.
“Our nation needs to say clearly once again that using drugs will destroy your life.”
He said telling people the “terrible truth” about drugs would save lives and turn back the “surge” in crime that follows increased drug use.
Mr Sessions’ comments will raise concerns among supporters of marijuana legalisation in the US, who are keen to find out how the Government will approach the drug.
He has previously claimed that legal cannabis causes violent crime, despite a lack of evidence for his claim.
Eight states and the District of Columbia have already legalised marijuana for recreational use. But the Justice Department would have several options available should it decide to enforce federal law.
These include filing lawsuits on the grounds that state laws regulating pot are unconstitutional because they are preempted by federal law.
While marijuana dependence is a growing problem, it actually “produces dependence less readily than most other illicit drugs”.
“Some 9 per cent of those who try marijuana develop dependence compared to, for example, 15 per cent of people who try cocaine and 24 per cent of those who try heroin,” a study found.