Prevalence and correlates of exceeding the labeled maximum dose of acetaminophen among adults in a U.S.-based internet survey.

Purpose: Acetaminophen is a commonly used analgesic; excessive doses can lead to liver damage. We sought to determine the proportion of acetaminophen users exceeding the recommended maximum daily dose of 4 g and identify correlates of such behavior.

Methods: U.S. adults were recruited from an internet panel in summer 2010, oversampling past 30-day acetaminophen users. Among 47 738 starting the study, 5649 completed all phases; individuals with low education were underrepresented. Subjects completed a 7-day daily diary online, reporting intake of acetaminophen products selected from a comprehensive list; total daily dose was computed from product names. An exit survey elicited: attitudes/knowledge related to product ingredients, label reading, dosing behavior; demographics, medical history, general physical, and mental health status. Unconditional logistic regression identified variables independently associated with use exceeding 4 g.

Results: Among 3618 acetaminophen users, 163 took >4 g on ≥1 day (4.5%); the median dose was 5.5 g; 26 took >8 g (0.7%). >4-g users were characterized by chronic pain, poor physical status, and heavy use of medical care. Knowledge of ingredients and recommended OTC doses for all products taken was inversely associated with >4-g use (multivariable odds ratios [ORs] = 0.5-0.6), as was the attitude to start with the lowest dose (OR = 0.6). The attitude that users could choose their own dose was positively associated (OR = 1.3).

Conclusions: The results estimate the proportion of acetaminophen users exceeding 4 g in a group of U.S. adults, identify potentially modifiable attitudes and knowledge associated with such use, and characterize subpopulations at higher risk.