How (not) to inform patients about drug use: use and effects of negations in Dutch patient information leaflets.

Purpose: Under EU regulations, patient information leaflets (PILs) are required to be clear and understandable. Negations (e.g., not, no) are a linguistic aspect that may impact PIL comprehension, yet go unmentioned in these regulations. We conducted two studies to determine (1) how negations are used in Dutch PILs (study 1) and (2) the effects of negations on readers (study 2).

Methods: Study 1 was a content analysis of 30 PILs of different brands of pollinosis drugs, half of which were freely available in drugstores and half only by physician prescription. We mapped negation use in PIL sections on 'proper usage' and 'potential side effects'. Study 2 was an experiment in which participants (N = 80, Mage  = 33.19 years, SDage  = 13.66; 76.3% female) were presented with one of two PIL texts on proper drug usage. Texts were identical except for the use of negations. After reading, participants answered questions about comprehension, PIL appreciation and medical adherence intentions.

Results: Study 1 demonstrates that negations are often used in PILs as 21.0% of clauses contain at least one negation. This number is higher in sections related to potential side effects than proper usage. Study 2 demonstrates that negations decrease both actual and subjective comprehension. Negations also decrease PIL appreciation and medical adherence intentions. The reduction in medical adherence intentions is driven by the decrease of subjective and not actual comprehension.

Conclusions: In general, participants prefer PILs that contain clear and comprehensible language. To increase comprehensibility, PIL designers should refrain from using negations as much as possible.