Regulation has been unscientific and too restrictive. But the spectre of psychosis means some will always have to be wary
Occasionally during my love affair with marijuana I would experience perceptual disruptions profound enough to freak me out. One time I was driving along a crowded road when my car seemed a little wobbly and then listed towards the centre, an alarming thud-thud emanating from the back end. In the middle of a densely populated spot without a hard shoulder, I crept slowly across a few lanes of traffic and pulled to a stop. Concentrating very hard, I got out of the car to assess and hopefully change the flat tyre. I rarely got paranoid from smoking weed; neither did it typically make me sleepy. Instead, I was among the lucky ones, as the drug made everyday activities such as gardening, waiting on tables and talking to my family bearable if not interesting. So I was shocked and embarrassed to find, after a few minutes of close inspection amid the honking horns, that there was nothing wrong with the car.
At the time I took hallucinations as evidence of a good score. Now, as an ex-smoker and neuroscientist whose focus is addictive drugs, I know that my resilient response to this stressful experience was contingent on having a neurotypical brain. Neural pathways are forged by finely orchestrated signals for synapse growth and pruning; disruptions can result in atypical neural connections that increase the risk of psychosis. The liability may be unmasked by environmental conditions that can essentially be reduced to an ambiguous but well-recognised bogeyman: stress.