Last week Professor Roger Pertwee called for cannabis to be licensed for sale, and now Tim Hollis, the Association of Chief Police Officers' lead officer on drugs, has said the current criminalisation-based approach to policing cannabis use should be reviewed. Pertwee and Hollis are bringing a welcome breath of fresh air to the debate about drugs and the harm they do.

The government now has the chance to take a genuinely science-based approach to drugs policy. Labour took an extremely distorted and punitive view of cannabis. It rejected both scientific evidence and public opinion that its harms were relatively modest and reclassified it to Class B status under the 1971 Misuse of Drugs Act so that possession for personal use can now result in up to five years in prison. Worse, Labour also instigated a policy of pursuing users with an almost religious fervour with police sniffer dogs assisting in interventions at tube stations and other places where users might be easily sequestered and searched.

Why was this done? It appears that Labour believed that cannabis was very harmful to mental health; especially that it caused schizophrenia. Yet as the advisory body the ACMD pointed out in its 2008 cannabis review, to stop one case of schizophrenia more than 5,000 young men would have to be prevented from ever using cannabis. This statistic negates any meaningful value in controlling cannabis to improve mental health.

Labour also held the view that punishment would reduce use and hence harms. There is no meaningful evidence in favour of this view. The evidence we do have – for example, from the experiences with decriminalisation in the Netherlands and some Australian states – is that decriminalisation leads to a reduction in harms.

Science cannot determine alone what the framework for drugs regulation should be. But if policy is not grounded in the science it can easily collapse into prejudice, moralism and authoritarianism. The chaos earlier this year over the "legal high" mephedrone raised very significant issues of evidence in relation to new drugs of unknown harm. Alcohol is legal yet is producing growing levels of damage which are well detailed in government reports but recommendations for harm reduction are not acted upon. A recent scientific review of drug harms, originally published in The Lancet, found that many class A drugs are in fact less harmful than alcohol. This raises further questions over the coherence of current drugs laws.

In the face of a rising tide of dissatisfaction with the intellectual rationale for the current drugs laws, the coalition should seize the opportunity to establish a genuinely science-based approach to drugs policy.