Most people agree that the use of heroin, cocaine and amphetamines such as speed and ice can become highly addictive and, when they do, a lot of harm is done to users and their families.

So most of us agree that governments should be working to limit the use of such harmful drugs. The arguments come over how best to do it. The conventional approach is to make the production, importation, distribution, sale and consumption of such drugs illegal. Problem solved.

But we've been pursuing this prohibition approach for years, spending a fortune on policing, the courts and the high proportion of drug offenders in our jails. With all this has gone a fair bit of police corruption.

And yet illegal drug use remains widespread, with still too many drug overdoses and drug deaths. The seizures, arrests and prison sentences roll on, seemingly to little effect. People may be using less heroin, but its place has been taken by ice which, if anything, seems worse.

If prohibition so clearly isn't working, shouldn't we try a different approach?

Last week the NSW Bureau of Crime Statistics and Research published research that seems to provide powerful support for the contention that the conventional approach is broken.

We've all seen TV news reports of police proudly displaying the seemingly huge quantity of drugs they've just seized after an intricate detection operation. We're told the "street value" of the seized drugs, with the implication that this success will put a hole in drug consumption.

The take-away message is clear. See? The tide has turned and we're winning the war after all.

But the study took the figures for seizures and arrests of suppliers of illegal amphetamines, cocaine and heroin, and compared them with the figures for two indirect measures of drug use: hospital emergency department admissions for drug overdoses and arrests for drug use or possession. The figures were for the whole of Australia, over the 10 years to June 2011.

The study found no evidence that increases in drug seizures and arrests of drug suppliers reduced the number of emergency department admissions or the number of arrests for use or possession.

The study also analysed three specific NSW police operations – named Balmoral Athens, Tempest and Collage – identified by the NSW Crime Commission as being so successful they had the potential to affect the market for cocaine.

It found that the three operations did have the effect of reducing arrests for use or possession of cocaine, but the effect was only temporary.

In fact, the study found that increases in drug seizures were often associated with increases in hospital admissions and arrests of users. Huh? The likely explanation is that at times when there is a lot more of the drugs available, the police will be able to increase the amount they seize.

What more proof do you need? Prohibition isn't working and we should try something else. Many medical people would like to see less emphasis on criminalisation and more on harm reduction. Just imagine if we could take all the money poured into catching and punishing people and use it to help people get off drugs and sort out their lives.

But Dr Don Weatherburn and the other authors of the study argue strongly against using its findings to conclude that drug law enforcement is a waste of money.

Why not? Because, when you look at the issue the way an economist would, you realise there's more to prohibition that just attempting to stamp out all illicit drug use.

The other thing it does is force up the price of drugs. Research suggests the black-market price of cocaine in the United States is between 2 1/2 and five times what it would be in a legal market. For heroin it was between eight and 19 times higher.

Economists, as you know, are great believers in the power of prices, and in using prices to change people's behaviour. There's little reason to doubt that the high price of illegal drugs hugely reduces the number of users and the amount each user uses.

Before we write off prohibition we need to consider what economists call the "counterfactual": what would the world be like if these drugs weren't outlawed? Far more people would be using them and the amount of harm needing to be reduced would be almost infinitely greater.

But the law-enforcers need to remember what it is that's keeping the price of drugs so high. It's obviously not their success in greatly limiting the supply of drugs relative to the demand.

No, it's the high incomes drug producers and traffickers need to earn to induce them to run the great risk of imprisonment that working in this industry entails. As an economist would think of it, it's the big "risk premium" suppliers add to the prices they charge that keeps prices so high.

This suggests that rather than trying to maximise the size of the seizures they can parade on telly to prove how successful they are, law enforcers should maximise the risks of traffickers getting caught, thereby inducing them to charge a higher risk premium.

Ross Gittins is economics editor.

SMH