Cannabis – and specifically the use of cannabis oil – has been in the news a lot lately, spearheaded by the mother of epileptic Billy Caldwell, who had been successfully treated with oil containing THC but then denied it when his mother had the medical substance from Canada confiscated at the UK border. Science can be quite sniffy about single case studies like Billy Caldwell’s, viewing this as “low status” evidence compared to other methods of research. But many critical discoveries have been made by experiments based on one person. The way Charlotte Caldwell presented the effectiveness of cannabis oil in reducing her son Billy’s seizures has produced changes in government thinking that science has failed to do, despite decades of work challenging the legal status of cannabis.
The Caldwell case has ignited not one, but two debates about cannabis: whether it should it be legalised, and what the medicinal benefits of the drug – or indeed all illegal drugs that still might be medically useful – actually are. Both debates should be informed by evidence. Evidence should help cut through all the noise that often accompanies those who have strongly held views on either side of the argument.
The home secretary has said he will rely on evidence in his review of the potential health benefits of cannabis, but has ruled out any such parallel review of the recreational use of cannabis. Whenever someone refuses to use evidence for a review, we have to question why.
Evidence-informed policy is a relatively new idea in politics, and explains why we might be in the mess we are now in relation to cannabis. The 1971 Misuse of Drugs Act, which restricted the use of cannabis in the first place, was legislation constructed in an evidence-free way. Since then, all governments have inherited a regulatory system that has been informed more by politics than facts.
For example, the link between cannabis and mental health is often cited by the home secretary as justification for keeping it criminalised. But research exploring this relationship is messy, as among other problems, people tend to use more than one drug so we can’t absolutely establish causal relationships. It’s also never been clear whether people with conditions like schizophrenia are more likely to use cannabis because it controls their symptoms, or whether cannabis causes schizophrenic symptoms in the first place: as is often said in science, correlation doesn’t always mean causation.