Can a probiotic help you sleep? A randomized trial says maybe
What if the bacteria in your gut had something to do with how well you sleep?
Sounds like something you'd see on a wellness blog, but a randomized controlled trial published in May 2026 in Nutrients has some actual polysomnography data to back it up. A probiotic strain called Bacillus coagulans IDCC 1201, taken daily for four weeks, improved sleep efficiency by nearly 14 percentage points compared to placebo.
What the study did
A Korean team recruited 80 adults (ages 19–65) who reported sleep difficulties and randomly assigned them to take either a capsule containing 5 billion CFU of B. coagulans IDCC 1201 or a look-alike placebo, daily for four weeks. Double-blind — neither participants nor researchers knew who got what.
78 people finished the trial. The primary endpoint was change in PSG-measured sleep efficiency.
What the data showed
The results are notable:
Sleep efficiency improved by 13.71% in the probiotic group versus essentially no change (-0.15%) in the placebo group. Statistically significant (p = 0.002).
Total sleep time: the probiotic group gained nearly 50 minutes. The placebo group stayed flat.
Wake after sleep onset: the probiotic group reduced nighttime wakefulness by 44 minutes. The placebo group actually got slightly worse.
Sleep architecture shifted too — the probiotic group showed greater increases in stage 2 and REM sleep duration.
Subjective ratings matched: the Pittsburgh Sleep Quality Index improved more in the probiotic group (5.87 vs. 8.28 at week 4).
No significant safety concerns were identified.
Why gut bacteria might affect sleep
The short version: the gut-brain axis. Gut microbes can produce precursors to neurotransmitters, including tryptophan — the raw material your body uses to make serotonin and melatonin. You know, the hormone that tells your body it's time to sleep.
B. coagulans is a lactic acid-producing spore-forming bacterium. Some research suggests it may influence tryptophan metabolism by altering gut microbiome composition. But which pathway, which step — this paper doesn't dig into that.
Limitations
Small sample — 80 people, four weeks. We don't know about long-term effects, whether other probiotic strains would work, or whether this helps people with severe insomnia.
Also: the study was funded by the probiotic manufacturer. That doesn't mean the data is wrong, but it's worth knowing.
What this means for you
If you have mild sleep trouble and don't want medication, probiotics might be worth a try. Don't expect them to fix serious insomnia — this is one small, short study.
And not all probiotics are equal. This study used one specific strain (B. coagulans IDCC 1201). The bottle at your local pharmacy may contain something completely different.
FAQ
Q: Can I just buy probiotics and try this? A: You can, but check the strain. This study used B. coagulans IDCC 1201 specifically.
Q: How long until it works? A: This study ran for four weeks. Some people might notice changes earlier or later.
Q: Any side effects? A: No significant adverse events in this study, though some people may experience mild GI discomfort.
Q: Is it better than melatonin? A: No head-to-head comparison exists. Mechanistically, probiotics work more indirectly — via gut modulation → tryptophan → melatonin, rather than supplementing melatonin directly.