Iowa Code Title III. Public Services and Regulation [Chs. 80-122C] § 85.16. Willful injury--intoxication

(1) If the employer shows that, at the time of the injury or immediately following the injury, the employee had positive test results reflecting the presence of alcohol, or another narcotic, depressant, stimulant, hallucinogenic, or hypnotic drug which drug either was not prescribed by an authorized medical practitioner or was not used in accordance with the prescribed use of the drug, it shall be presumed that the employee was intoxicated at the time of the injury and that intoxication was a substantial factor in causing the injury.

(2) Once the employer has made a showing as provided in subparagraph (1), the burden of proof shall be on the employee to overcome the presumption by establishing that the employee was not intoxicated at the time of the injury, or that intoxication was not a substantial factor in causing the injury.