Aims To assess the role of drug violations in aviation accidents.
Design Case–control analysis.
Setting Commercial aviation in the United States.
Participants Aviation employees who were tested for drugs during 1995–2005 under the post-accident testing program (cases, n = 4977) or under the random testing program (controls, n = 1 129 922).
Measurements Point prevalence of drug violations, odds ratio of accident involvement and attributable risk in the population. A drug violation was defined as a confirmed positive test for marijuana (≥50 ng/ml), cocaine (≥300 ng/ml), amphetamines (≥1000 ng/ml), opiates (≥2000 ng/ml) or phencyclidine (≥25 ng/ml).
Findings The prevalence of drug violations was 0.64% [95% confidence interval (CI): 0.62–0.65%] in random drug tests and 1.82% (95% CI: 1.47–2.24%) in post-accident tests. The odds of accident involvement for employees who tested positive for drugs was almost three times the odds for those who tested negative (odds ratio 2.90, 95% CI: 2.35–3.57), with an estimated attributable risk of 1.2%. Marijuana accounted for 67.3% of the illicit drugs detected. The proportion of illicit drugs represented by amphetamines increased progressively during the study period, from 3.4% in 1995 to 10.3% in 2005 (P < 0.0001).
Conclusions Use of illicit drugs by aviation employees is associated with a significantly increased risk of accident involvement. Due to the very low prevalence, drug violations contribute to only a small fraction of aviation accidents.