Background: Herbal and supplementary products are widely used as sleep aids worldwide. We investigated the impact of a nutraceutical formulation on objective and subjective sleep parameters among adults with mildly impaired sleep.Methods: 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. The primary outcome was change in sleep efficiency (total time asleep/total time in bed [%]). We also assessed other actigraphic outcomes, PSQI, health-related quality of life measured with the SF-36 questionnaire, and salivary cortisol. Analyses were done by intention-to-treat. This study was registered at clinicaltrials.gov under number NCT05609890.Findings: 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.Interpretation: Among adults with mildly impaired sleep, a nutraceutical combination did not improve objective or subjective sleep parameters more than a placebo infusion. Combined with previous evidence, our results suggest that many of the positive effects of herbal supplements on sleep may result from factors unrelated to their composition.Trial Registration: This study was registered at clinicaltrials.gov under number NCT05609890.Funding: This study was funded by Team Foods Colombia.Declaration of Interest: Team Foods provided funding for the study in the form of an Investigator- Initiated award, but had no influence on the conduct or analysis of the study, or on the decision to publish.Ethical Approval: The study protocol was approved by the IRB Riesgo de Fractura S.A., according to minute CEI-51 of December 15, 2022. All participants underwent an informed consent procedure and provided written informed consent before participation. All study procedures were executed in compliance with regulations for health research dictated by resolution 8430-1993 of the Colombian Ministry of Health and with the principles stated by the Helsinki Declaration of 1964 and its later amendments.