There are two things I know about marijuana. They are two separate and different things, and I wish that they could be kept that way.

Firstly, there are chemicals which can be extracted from cannabis plants which have some medicinal value. They are probably useful for nausea, for pain, for nervous conditions and maybe for a whole host of other things.

Secondly, some people like to smoke pot or bake with weed. It is one of those things, like supersizing your fries, drinking more than a couple of beers, boxing or riding a motorbike that comes with a small health risk, but which is generally considered to be acceptable when done by adults in moderation.

My problem is when people try to mix these two things and expect physicians to prescribe marijuana for health reasons. That is not how modern medicine should work. There are no other herbal products which medical doctors are expected to know anything about, to use or to prescribe.

When people have severe pain we don’t expect them to find an opium poppy grower, we give them IV morphine, a pure drug extracted from the juice of the opium poppy. When you come to the emergency department with a heart attack, the physician does not run into the stock room and start grinding up dried foxgloves, but instead injects pure digoxin. If I am giving an anesthetic and the surgeon asks for more muscle relaxation, I don’t have to check if a shipment of Chondrodendron tomentosum has arrived from South America. I just open a vial of Rocuronium, a synthetic drug similar to the curare originally found in arrow poisons made from the Chondrodendron tomentosum vine.

Why is marijuana treated so differently from any other herbal medicine? Scientists are very good at extracting the pure active ingredients from herbal medicines. This year, the Nobel prize for medicine went to a Chinese doctor for her work on extracting the anti-malarial drug, Artemisinin, from the Wormwood plant. There are already some pills made of pure chemicals extracted from cannabis plants, and we need to work on developing more and better such medicines.

Doctors should prescribe pure medical substances in pills, potions, and ampoules. Herbalists should provide herbal medicines. And if some stores want to call themselves dispensaries and sell stuff to adults that make them feel good, then let them go for it. I do not see it as part of a physician’s responsibility to prescribe an herbal medicine of unknown composition or strength or purity on the basis of a patient’s assertion that it makes them “feel better”.