Reported Side Effects and Adherence of Daily HIV Pre-Exposure Prophylaxis Users in Ontario, Canada: An Analysis of the Ontario Pre-Exposure Prophylaxis Cohort Study

Side effects are a common concern of current and potential HIV pre-exposure prophylaxis (PrEP) users, potentially leading to missed doses. We examined the relationship between reported side effects and adherence in the Ontario PrEP Cohort Study (ON-PrEP). In total, 600 predominantly gay (87.3%), White (65.8%), and male (95.0%) participants completed questionnaires assessing the presence and severity of five side effect categories (nausea, diarrhea, headache, abdominal pain, and "other") as well as their adherence to daily PrEP (any missed doses in the previous 4 days). In total, 175 participants (29%) ever reported experiencing side effects: most commonly diarrhea (7.5% of study visits), and most were of mild severity. Lower incomes (<i>p</i> = 0.01), identifying as bisexual (<i>p</i> = 0.04), and baseline concern about side effects (<i>p</i> < 0.001) were associated with ever reporting side effects. The odds of reporting any side effects decreased by a factor of 0.44 (95% confidence interval 0.25-0.80) with each additional year of PrEP use, however 1 in 10 participants still reported side effects after 1 year of use. The odds of reporting optimal adherence were 0.48 (0.28-0.83) times lower for participants reporting any side effects, 0.67 (0.51-0.89) times lower per additional side effect category reported, and 0.78 (0.65-0.97) times lower per incremental increase in side effect severity ratings. We found some evidence of interaction between side effect measures and duration of PrEP use, suggesting that these relationships were stronger for participants taking PrEP for longer. Clinicians should make efforts to ascertain patients' experience of side effects and consider risk counseling and alternative PrEP regimens to promote adherence.