The war on drugs has been a $1tn failure. For more than four decades, governments around the world have pumped huge sums of money into ineffective and repressive anti-drug efforts. These have come at the expense of programmes that actually work such as needle exchanges and substitution therapy. This is not just a waste of money, it is counterproductive.

The London School of Economics has just completed perhaps the most thorough account of the war on drugs done to date. The conclusion, backed by five Nobel Prize-winning economists: it has done more harm than good.

Drug prohibition has created an immense black market, valued by some at $300bn. It shifts the burden of “drug control” on to producer and transit countries such as Afghanistan and Mexico. This approach also fails to grapple with a basic truth: drug markets are highly adaptive. Repress the business in one country and it springs up elsewhere.