The WHO is the world's leading health organisation guiding governments around the world. So we expect their advice to be up to date and evidence-based, particularly on controversial topics. One of the most controversial topics of our time is the international community's approach to drug policy, particularly that relating to the most popular so-called "illegal" drug – cannabis. Yet the WHO's advice on the harms and (lack of) benefits of cannabis is based on a decision made 82 years ago, by its predecessor, the League of Nations. Thankfully, there is now hope that this is about to change.

The WHO advises the UN, which states international control of drugs – so the view of the WHO really matters. The reality is that almost every country in the world (197 in total) sign up to follow WHO advice and so its current stance means punitive measures for cannabis – including lifetime in prison in some countries. Cannabis is still scheduled as having the highest level of harm and no medical value, despite reams of evidence to contrary. It is significantly less harmful than alcohol and shows real medical benefit, particularly in the treatment of pain, spasticity, and some forms of epilepsy. Due to these therapeutic effects, over 18 countries and over 200 million US citizens now have access to licensed medicinal cannabis. Consequently, the idea that cannabis isn't a medicine is considerably less plausible now than when this decision was made in 1934. Worse still, the actual report on which cannabis was scheduled in 1934 can no longer be found so it may be that the decades-long ban on cannabis is based on real errors of fact!

What is equally problematic is that the current legal status of cannabis means that research into its potential benefits – or harms - is really tough because of the regulations that accompany its Schedule 1 status. For example, in the UK medical researchers like me need a special license to hold cannabis for research though as a doctor I can prescribe heroin - a much more dangerous and sought-after drug. The UK government believes that it can't change this prohibitionist position and still comply with the UN conventions. This is untrue, as The Netherlands has demonstrated for over 30 years, but the easiest way to get a change in the UK policy would be if the WHO led the way.

It is vital that experts take all latest data into account during such a vital review, and to this end DrugScience has produced a detailed up-to-date assessment of cannabis for the public as well as the WHO and UN. This report authored by 4 experts – two from DrugScience - provides the vital background evidence on which a sensible modern re-assessment of cannabis can be made. This should lead to an appreciation that cannabis has medical value in some illnesses, and so encourage research into its potential for others, such as cancer, ADHD and PTSD. A proper review of cannabis could also encourage a more nuanced view of the comparative harms of different forms of cannabis, helping direct users away from the strong d9THC/low cannabidiol variants such as "skunk" that appear significantly different from more traditional herbal or resin forms of cannabis.

Big issues like this need that affect hundreds of millions of people across the globe need to determined based on the best and most current evidence available. Leading organisations such as the WHO and UN need to be able to move quickly to try and avoid the public losing out.

At last there has been some progress! This came from the recent meeting of the WHO Expert Committee on Drug Dependence in the WHO headquarters in Geneva. Here the Expert Committee and the WHO Lead for Medicines, Dr Suzanne Hill, were presented with the report by the DrugScience team. They also heard powerful supporting arguments from two other expert groups (the International Drug Policy Consortium and the International Association for Hospice & Palliative Care) both of whom also made it clear that there was a pressing need for a review of cannabis scheduling.

The DrugScience team argued that the Expert Committee had the right to change its agenda to start a full pre-review of cannabis immediately based on our WHO-standard report. This they declined to do, but it seems our arguments were heeded as an official pre-review has been ordered, to be completed before the next meeting of the Commission on Narcotic Drugs in 2018.

This move by the WHO is encouraging as its perception as being an evidence-based health organisation has become seriously questioned by its failure to consider the evolving facts on cannabis. It is critical that the review they conduct is honest, transparent and fully evidence-based; for surely then it will be impossible for the UN to continue to argue that cannabis should be scheduled as being extremely harmful and lacking medical value!