A Longitudinal Study of Cannabis Use Increasing the Use of Asthma Medication in Young Norwegian Adults

Jørgen G. Bramness; Tilmann von Soest


BMC Pulm Med. 2019;19(52) 

In This Article


This study combined survey data and data from a national prescription registry to demonstrate that the filling of presciptions for asthma medications was related to current, but not former, cannabis use. The odds for filling a prescription increased two-fold for current cannabis users compared to those who had never used cannabis and this increased odds withstood adjustment for all other relevant risk factors, such as female gender, self-reported asthma and allergies in adolescence, and even daily smoking in a comprehensive regression model.

The use, in our study, of prescription of asthma medication as outcome measure is novel, but our finding is in line with several studies indicating a negative effect of cannabis use on respiratory function and the precipitation of asthma.[13,16,24–27] We found an increase of approximately 70% in the prescription of asthma medication among cannabis users. This increase is comparable to other studies which have found similar levels of increased risk.[13,16,26,27]

The validity of the study design and the findings was strengthened by fact that the study identified that participants' self-report of having asthma at an earlier time point was, in itself, a risk factor for filling a prescription for asthma medications. Study findings are also in accordance with previous studies by showing thatpreviously identified risk factors such as female gender,[6] tobacco smoking[4] and at a trend level BMI[5] increased the odds of asthma medication being prescriped. Controlling for these factors only marginally changed the relationship between cannabis use and filling a prescription for asthma medication. We cannot ultimately rule out the possibility of residual confounding. We were, however, able to control for having allergies, a known risk factor for asthma,[1] but this still did not change the impact of current cannabis use on asthma. We have found no other studies investigating the relationship beween cannabis use and asthma medication that have been able to adjust for self-reported allergies.

Our study also indicated no effect of former (but not current) cannabis use on asthma medication prescription. Former use could indicate people who have only tried cannabis, an exposure less likely to have negative health effects. As we lack measures on the amount of cannabis used, this finding should be interpreted cautiously, but it may be in line with earlier suggestions that quitting cannabis is beneficial for lung function and reduces asthma symptoms.[26]

Our study cannot completely rule out the possibility of reversed causality, i.e. that patients with asthma use cannabis to relieve symptoms. Some studies do show that cannabis may relieve symptoms of airway obstruction and asthma.[10,17–21] However, our results show that asthma in adolescent years (at T1) was not related to cannabis use. Moreover, we did adjust for asthma at an earlier time point in our study. It is still possible that people are using cannabis to alleviate asthma symptoms, without a formal diagnosis of asthma or awareness of having the condition.

The study had a sufficiently large cohort of young adults with enough exposure to cannabis in order to detect potential negative effects of cannabis use. The national coverage of NorPD ensured complete data for prescriptions filled. We do not know, however, if prescribed drugs were in fact used, as we have no information of secondary non-compliance. Furthermore, filling a prescription for asthma medication is not the same as a diagnosis of asthma. A prescription is only a proxy for the disease. Investigations show that asthma may be undertreated,[33] and this may lead to an under-estimation of a diagnosis of asthma. We have no information regarding whether such under-treatment should be more or less severe among cannabis users, and do not know if this has introduced a bias. Furthermore, the responders were followed for a sufficient time to pick up on negative health effects, as we followed the respondents' prescription records up to 9 years after the last questionnaire. However, the study is limited by not providing information about how much cannabis participants had used or if they were using cannabis in the whole time period.