Cannabis is very widely used, particularly by people who later show signs of psychosis; as to whether use of cannabis actually causes a 40% increase in the development of psychosis, I don’t suppose we shall ever be completely sure. This much-discussed systematic review is laudably cautious in its conclusions. Maybe on the whole cannabis is better avoided, and perhaps the best social policy would be regulated availability, so that people who wish can obtain the weaker varieties with due warning.

Some years ago, Alec Logan asked me to write a column for the back pages of the BJGP, which I called Flora Medica, ending with something arcane and amusing from the lesser medical literature. I soon realised that if all else failed I could always turn to journals of occupational allergy, since anything can trigger asthma in the workplace, including boiling broccoli, as I found in one paper. Here a rigorous prospective cohort study (the European Community Respiratory Health Survey, ECRHS-II) finds that after jobs that involve exposure to smoke and chemical spills, nursing carries the highest risk for the development of asthma. But why? Do nurses boil a lot of broccoli?

This seminar points out that chronic myeloid leukaemia was the first cancer to yield to genetically tailored therapy – imatinib. It is a rare disease, occurring in a scattering of mostly elderly people, the great majority of whom can be cured using this drug. If one of them happens to be a patient of yours, this is the place to read about it.

Although in-vitro fertilisation has now been carried out for 30 years, we are still learning about its long-term outcomes, especially as the largest cohort has yet to reach adulthood. In the short term, multiple birth provides the biggest range of hazards. The leading congenital abnormality associated with assisted reproduction is urogenital malformation in boys, but there are wide confidence intervals for the overall risk of malformation, and the risk is unlikely to be more than 30% above unassisted gestation. As far as social discord within families goes, there is no increase at all, despite the emotional strain and financial cost which IVF commonly brings.