The trial, registered with the Clinical Trial Registry of India, enrolled healthy adults aged 18 to 70 with Pittsburgh Sleep Quality Index scores between 5 and 15, indicating mild to moderate sleep complaints. Each participant took both treatments in sequence, one week each, separated by a seven-day washout. Because the two products looked different, the team used a double-dummy design: everyone swallowed a capsule and a tablet every night at 9:30 p.m., one active and one placebo, so that neither participants nor investigators knew who was getting what. All 24 participants completed both phases, with no withdrawals or protocol deviations.

The centerpiece of the study was an unusually demanding measurement protocol. Researchers inserted a peripheral venous catheter into each participant and drew blood at fixed intervals from 5 p.m. to 5 a.m. under dim light conditions of less than 8 lux, then measured plasma melatonin using ELISA. From these profiles they calculated the dim-light melatonin onset, or DLMO, the moment when melatonin concentrations cross and stay above a threshold of 10 picograms per milliliter. DLMO is widely regarded as the gold-standard marker of central circadian phase, essentially a timestamp for the body’s internal clock.

At baseline, participants’ melatonin levels crossed the 10 pg/mL threshold around 11 p.m. After a single dose of the black cumin extract, that onset shifted to 10 p.m., and after seven consecutive nights it advanced further to roughly 9:30 p.m. That represents a progressive advance of the circadian clock of up to 90 minutes, achieved without administering any melatonin at all. The researchers could not interpret the corresponding threshold crossing in the melatonin arm as a true DLMO shift, because the measured plasma levels there were dominated by the exogenous supplement itself.

The shape of the two melatonin curves told two very different stories. Synthetic melatonin produced a dramatic surge, with plasma concentrations jumping roughly 138-fold within 30 minutes of ingestion, from about 7.5 to over 1,000 pg/mL, followed by a steep decline as the compound was cleared. The black cumin extract, by contrast, produced a gradual, sustained rise: single doses lifted melatonin from about 9.6 pg/mL at 10 p.m. to 114.6 pg/mL by 3 a.m., and seven days of repeated dosing pushed levels to 148 pg/mL at the same time point, increases of up to nearly 190 percent over baseline. By 3 a.m. and 5 a.m., the two treatments produced statistically indistinguishable melatonin levels, suggesting the plant extract sustained endogenous secretion across roughly six hours rather than delivering a transient pharmacological spike.

Sleep itself was tracked objectively with wrist actigraphy, a watch-like device worn continuously for seven days that estimates sleep latency, total sleep time, wake after sleep onset, and sleep efficiency. Both treatments significantly improved all of these parameters over the week. The details favored each compound in different respects: synthetic melatonin produced somewhat faster sleep onset, while the black cumin extract was associated with a mean increase of about 12.6 minutes in total sleep time. Sleep efficiency and nighttime waking were statistically comparable between the two by day seven.

Two secondary findings may prove the most consequential. First, the black cumin extract significantly reduced serum cortisol, the body’s primary stress hormone, from an average of 25.2 to 19.8 micrograms per deciliter over the week, an effect with a large treatment-by-time interaction. Synthetic melatonin left cortisol essentially unchanged. The authors point to the hypothalamic-pituitary-adrenal axis and the arousal neuropeptide orexin as plausible mechanistic targets, noting earlier work suggesting the extract can dampen stress signaling. Chronic hyperarousal is considered a central driver of insomnia, so a supplement that lowers cortisol while raising melatonin addresses the stress-sleep-circadian axis from both ends.

Second, daytime sleepiness, measured with the Epworth Sleepiness Scale, fell significantly with the black cumin extract but not with melatonin. Among the nine participants who reported clinically relevant sleepiness at baseline, seven days of the extract cut scores by 25.7 percent, while melatonin produced no significant improvement. This matters because daytime grogginess is one of the most common complaints associated with melatonin supplements, particularly at doses of 3 to 5 milligrams and above. In this trial, ten participants reported adverse events during the melatonin phase, including lightheadedness, palpitations, headaches, and gastrointestinal discomfort, whereas the extract phase produced only two mild, self-limiting cases of bloating and one flu-like illness judged unrelated to treatment.

The contrast arrives amid growing scrutiny of melatonin supplementation. Global production of the hormone was estimated at around 4,000 metric tons in 2019 and is growing by more than 10 percent annually, yet large-scale long-term safety trials in adults and children remain scarce. Regulatory agencies in France and Canada have flagged inconclusive concerns about melatonin and sudden infant death syndrome, and observational findings presented at the American Heart Association’s scientific sessions have suggested a possible association between long-term melatonin use and heart failure diagnoses. Scientists also worry that supraphysiological melatonin levels may desensitize the MT1 and MT2 receptors in the brain’s suprachiasmatic nucleus, potentially blunting responsiveness to the body’s own hormone over time.

The authors are careful to note the study’s limits: only 24 participants, a short one-week intervention per arm, healthy volunteers rather than clinical insomnia patients, and lifestyle factors such as caffeine and screen exposure that were not tightly controlled. Significant sequence and period effects appeared for some repeated-dose outcomes, though the overall interpretation held. Still, the core message is provocative. Rather than flooding the bloodstream with an external chronobiotic, a thymoquinone-rich oil extracted from a seed used for centuries in Indian and Arabic traditional medicine appears to nudge the body’s own neuroendocrine machinery, advancing the circadian clock, sustaining natural melatonin through the night, lowering cortisol, and sharpening daytime alertness. Larger and longer trials will be needed before black cumin extract can be recommended as a melatonin alternative, but this small crossover study offers the most rigorous physiological evidence yet that the spice rack may hold a genuine modulator of the circadian axis.

Subject of Research: A randomized crossover trial comparing black cumin oil extract with synthetic melatonin for circadian regulation and non-restorative sleep

Article Title: Responsiveness of ThymoDream® as a natural modulator of the circadian axis: a comparative RCT with melatonin supplementation employing melatonin profiling and actigraphy

Article References: Responsiveness of ThymoDream® as a natural modulator of the circadian axis: a comparative RCT with melatonin supplementation employing melatonin profiling and actigraphy. (n.d.). https://doi.org/10.3389/frsle.2026.1879110

Image Credits: AI Generated

DOI: 10.3389/frsle.2026.1879110

Keywords: black cumin, Nigella sativa, thymoquinone, melatonin, circadian rhythm, DLMO, sleep quality, cortisol, actigraphy, randomized controlled trial, HPA axis, non-restorative sleep