Abstract In this randomised, placebo-controlled trial, we assigned adults with a Pittsburgh Sleep Quality Index (PSQI) > = 5 to receive a formulation containing L-theanine (from green tea – Camellia sinensis extract), lemon balm ( Melissa officinalis ) extract, valerian ( Valeriana officinalis ) extract, and saffron extract ( Crocus sativus ), or placebo, during six weeks. We enrolled and randomised 64 individuals, of whom 31 from the active group and 27 from the placebo group completed the six-week follow-up. Mean sleep efficiency remained unmodified in the active group, and increased by 3% in the placebo group, the between-group difference in the change was not statistically significant (p = 0.49). Total sleep time also improved more with placebo (13.0 vs. 1.33 minutes, p = 0.66). Time wake after sleep onset (WASO) decreased more in the active group (4.6% vs. 2.4%), but the difference was not significant (p = 0.33). Mean PSQI decreased by 3.11 points (32.3%) in the active group, and by 3.86 points (39.5%) in the placebo group (p = 0.41). SF-36 increased more with placebo (+ 18.3 in active, + 32.1 in placebo, p = 0.68). Salivary cortisol remained unchanged in both groups. No serious adverse events were reported. Among adults with mildly impaired sleep, a nutraceutical combination did not improve objective or subjective sleep parameters more than a placebo infusion.