Asthma and chronic obstructive pulmonary disease (COPD) are widespread chronic conditions with medication frequently delivered by inhalers. These can be challenging to use correctly, but the scale of misuse and the specific aspects of failure are unclear.

We used systematic review methods to search 9 databases in May 2015 to identify and review studies that assessed adults (18 years or older) with asthma or COPD using inhalers of various types including pressurised metered dose inhalers (pMDIs), dry powder inhalers and the Respimat inhaler. Studies must have reported the scale of inhaler misuse, variation by type of inhaler or which steps patients had difficulty completing accurately.

The types of inhalers, inhaler interventions and definitions of failure and misuse varied widely in the 38 studies identified. It was not possible to draw conclusions on the differential failure rates between different types of inhalers or any patient characteristics.

Of the studies reporting failure or misuse rates, the majority ranged between 0 and 20%. Studies were inconsistent regarding the number of inhaler steps collected, reported and labelled as critical.

There is evidence for all identified inhalers that some people may be using them incorrectly, but it is unclear which inhalers have higher rates of misuse or which steps within the inhaler technique are most difficult for patients. The optimal techniques for using inhalers are not standardised. Researchers undertaking future inhaler studies are respectfully directed to our recommendations for future research.