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STUDY OBJECTIVE: To evaluate next-morning driving performance after middle-of-the-night use of zolpidem 3.5 mg in a buffered sublingual formulation (ZST). DESIGN: Single-center, four-period, randomized, double-blind, placebo-controlled, crossover study. SETTING: Maastricht University, The Netherlands. PARTICIPANTS: Forty healthy volunteers (20 females). INTERVENTIONS: Single dose of ZST administered in the middle of the night at 3 and 4 h before driving, zopiclone 7.5 mg at bedtime 9 h before driving, and placebo. MEASUREMENTS: Performance in a 100-km standardized highway driving test in normal traffic measuring standard deviation of lateral position (SDLP) - an index of weaving. Drug-placebo changes in SDLP > 2.5 cm were considered to reflect clinically relevant driving impairment. RESULT: For ZST, Max McNemar symmetry analyses showed that the proportion of drivers classified as impaired was increased 3 h after dosing (P < 0.012), but not 4 h after dosing. Mean increases in SDLP from placebo, although statistically significant, were small (1.46 cm [P < 0.0001] at 3 h and 0.83 cm [P = 0.0174] at 4 h). The morning after zopiclone, 45% of the drivers were classified as impaired with a mean increase in SDLP of 2.46 cm (P < 0.0001). There were no significant sex differences in effects of ZST and zopiclone. CONCLUSION: Zolpidem 3.5 mg in a buffered sublingual formulation has a minimal risk of impairing driving performance in the morning >/= 4 hours after middle-of-the night use. When taken 3 hours before driving, the drug may have impairing effects so caution should be exercised if medication is taken other than as indicated. CLINICAL TRIAL INFORMATION: ClinicalTrials.gov Identifier: NCT01106859; Trial Name: Driving Performance After Middle of the Night Administration of 3.5 mg Zolpidem Tartrate Sublingual Tablet; http://clinicaltrials.gov/ct2/show/NCT01106859. CITATION: Vermeeren A; Vuurman EF; Leufkens TR; Van Leeuwen CJ; Van Oers AC; Laska E; Rico S; Steinberg F; Roth T. Residual effects of low-dose sublingual zolpidem on highway driving performance the morning after middle-of-the-night use. SLEEP 2014;37(3):489-496.