Adding dexamphetamine did not make alcohol-impaired driving performance reliably safe in a controlled simulator study. A partial benefit on selected attention measures was not equivalent to reversing alcohol’s effects across driving tasks.
Simons and colleagues used a randomized crossover design with dexamphetamine 10 mg, alcohol 0.8 g/kg, their combination and placebo. Eighteen volunteers enrolled and 16 provided analyzable datasets. The simulator assessed lane control and risk-related behavior; separate tests assessed vigilance and divided attention. This was a human dosing experiment involving dexamphetamine, not methamphetamine.
Alcohol increased lane-position variability and changed accepted gaps. Alcohol alone and the combined condition were associated with more red-light running and collisions than dexamphetamine alone or placebo. Attention impairments were present with alcohol and, to a lesser degree, the combination. However, not every driving measure differed significantly in every comparison. It would overstate the data to describe the combination as equally impaired on all endpoints, just as it would be wrong to call the stimulant a successful antidote.
The sample was small and studied a particular dose combination, timing and simulator. The absence of a significant difference on one endpoint does not establish equivalence to placebo or safety in real traffic. Subjective stimulation, attention performance and collision-related behavior represent different outcomes. Alcohol concentrations changed during testing, so timing belongs with the exposure description. These findings do not yield a legal rule or a universal drug-concentration cutoff. They show why a person feeling more stimulated, or improving on a selected task, cannot be assumed to have recovered the full set of skills needed for driving.
See why measured drug concentration is not a simple performance scale.