Research Watch: What Recent Studies Say About Supplements for Stress and Cortisol

Welcome to the third Research Watch. Every Saturday I read the recent supplement research that crossed my desk and write up the studies worth knowing about. This week the topic is stress and cortisol, and one pattern kept repeating across the data. Cortisol is the number almost every stress supplement promises to lower, yet lowering it turned out to be a surprisingly poor predictor of whether people actually felt less stressed. Here is what the recent peer-reviewed evidence shows.

Quick Answer

Ashwagandha is the most studied stress supplement and reliably lowers cortisol, but a 2025 meta-analysis found that the cortisol drop did not translate into significantly lower perceived stress. Standardized ashwagandha extracts and multi-herb adaptogen blends do improve perceived stress in controlled trials, though many of those trials are industry funded. Psychobiotics show the mirror image: people reported feeling less stressed while cortisol stayed flat. The honest summary is that cortisol is one signal in a complex system, not the scoreboard, and the supplements with the best evidence work on how you feel and function, not just on a single hormone.

What This Week's Reading Covered

Stress supplements are a crowded, confident category. I stayed in recent randomized controlled trials and meta-analyses from 2023 to 2026, and I deliberately favored studies that measured both a biological marker, usually cortisol, and a subjective outcome, usually the Perceived Stress Scale or an anxiety rating. That combination is where the interesting tension lives. Six studies anchor this post, each linked to PubMed so you can read the abstract yourself. Where a study was funded by the company selling the ingredient, I say so.

Ashwagandha Lowers Cortisol, But That Did Not Lower Perceived Stress

The most important study this week is a 2025 systematic review and meta-analysis in Nutrition and Health. It pooled randomized controlled trials of ashwagandha and separated two questions that marketing usually blurs together: does it lower cortisol, and does it lower how stressed people feel. Across seven trials reporting cortisol and six reporting perceived stress (488 participants total, oral doses of 250 mg per day or higher for at least two weeks), the answer split.

Cortisol fell significantly, by 1.16 micrograms per deciliter (95 percent confidence interval minus 1.64 to minus 0.69, p less than 0.001). Perceived stress, measured by the Perceived Stress Scale, did not move significantly (standardized mean difference minus 0.355, 95 percent confidence interval minus 1.188 to 0.47, p equals 0.40). In plain terms, the hormone went down but the feeling did not reliably follow. The author flagged moderate heterogeneity (I-squared 50.9 percent) and noted that most trials were short, which is part of why the perceived-stress signal may be underpowered. Either way, it is a useful corrective to the idea that a cortisol number on a lab report is the same thing as relief.

Source: Albalawi AA. Nutrition and Health. 2025. PubMed 40746175

A Three-Arm Ashwagandha Trial Shows Why the Placebo Group Matters

A 2026 randomized, double-blind, three-arm trial in the Journal of Medicine and Life tested a proprietary ashwagandha root extract at 300 mg twice daily against a standard ashwagandha root extract and against placebo, in 141 healthy adults with moderate stress and anxiety, over 8 weeks. The primary endpoint was serum cortisol at week 8.

Here is the detail worth sitting with: all three groups, including placebo, showed a significant reduction in serum cortisol. Cortisol is sensitive to time, routine, and the simple fact of being in a study, so a before-and-after cortisol drop in a single arm is weak evidence on its own. Where the proprietary extract separated from placebo was on the subjective measures. It beat both comparators on the Perceived Stress Scale, the Hamilton Anxiety Rating Scale, the Oxford Happiness Questionnaire, and mood (all p less than 0.05). The honest read is that the felt-stress improvement is the more credible finding here, and that this is an industry study of a branded extract, so independent replication matters.

Source: West RE et al. Journal of Medicine and Life. 2026. PubMed 41815853

Adaptogen Blends: Rhodiola, Holy Basil, and Ashwagandha

A 2026 randomized, double-blind, placebo-controlled trial in Trials tested two plant-based formulas in 186 people with high stress over 60 days: one combining Rhodiola, holy basil, and Schisandra chinensis, and one full-spectrum ashwagandha. Both formulas significantly reduced Perceived Stress Scale scores versus placebo (p less than 0.0001), and both improved sleep quality on the Pittsburgh Sleep Quality Index and reduced anxiety. Neither changed self-reported mental alertness.

This is a genuinely positive result for adaptogen blends on perceived stress, and it reflects the kind of multi-ingredient approach a lot of people actually use. The caveat is funding. The trial was run and authored by a supplement manufacturer (Gaia Herbs). That does not invalidate the data, but it is exactly the context to keep in mind when a study testing a company's own formula reports a clean win.

Source: McKinney E et al. Trials. 2026. PubMed 41656269

Psychobiotics: Stress Relief Without Moving Cortisol

A 2025 randomized, double-blind, placebo-controlled trial in Foods approached the cortisol question from the opposite direction. Researchers gave 116 high-stress adults, mostly firefighters with elevated perceived stress, a dual-strain psychobiotic (live Lactobacillus plantarum PS128 plus heat-treated PS23) for 8 weeks. Compared with placebo, the supplement group showed significantly greater reductions in job stress, state anxiety, and insomnia severity (all p less than 0.05).

On the biology, serum adrenocorticotropic hormone and norepinephrine fell significantly, but cortisol did not change. So here people felt meaningfully less stressed while the headline stress hormone stayed flat. Put this study next to the ashwagandha meta-analysis and the lesson is hard to miss. Cortisol and the experience of stress can move independently, in either direction. A supplement that does not touch your cortisol can still change how stressed you feel, and a cortisol drop does not guarantee you will feel better.

Source: Lee MC et al. Foods. 2025. PubMed 41464897

An Honest Null: When Probiotics Did Not Beat Placebo

Not every gut-brain study lands, and the honest ones say so. A 2026 randomized, double-blind, placebo-controlled trial in Brain Sciences gave 100 healthy adults with self-reported anxiety a two-strain probiotic for 12 weeks. The primary endpoint, the Hamilton Anxiety Rating Scale, was not met. There was no significant effect on perceived stress or state anxiety versus placebo either. The one bright spot was a significant improvement in the vitality domain of a quality-of-life questionnaire, plus a non-significant trend toward lower depression scores.

I include this deliberately. Psychobiotics are a promising area, and the firefighter study above is encouraging, but strain, dose, and population matter enormously, and a different strain in a different group simply did not work. Reading the wins without the nulls is how people end up overestimating an entire category.

Source: Day R et al. Brain Sciences. 2026. PubMed 42041827

Saffron and the Acute Stress Response

The last study zooms in from weeks of supplementation to a single stressful moment. A 2023 randomized, double-blind, placebo-controlled crossover trial in Nutrients gave 19 healthy young men a single 30 mg dose of a saffron extract, or its main volatile compound safranal, or placebo, then put them through the Maastricht Acute Stress Test, a standardized laboratory stressor. Compared with placebo, saffron and safranal significantly reduced subjective stress and anxiety during the test, and delayed the time to peak salivary cortisol and cortisone (p less than 0.05).

This is a small, all-male, acute study, so it cannot tell us much about daily use over weeks. But it is a clean mechanistic snapshot. Saffron appears to soften the psychological hit of an acute stressor and reshape the timing of the cortisol response rather than simply flattening it. It is an early signal worth watching as larger trials accumulate.

Source: Pouchieu C et al. Nutrients. 2023. PubMed 37447245

What This Means for You

• Stop treating cortisol as the scoreboard. The strongest theme this week is that cortisol and felt stress can move independently. A lab cortisol number is a data point, not proof you will feel calmer, and a supplement that does not lower cortisol can still help.
• If you want the most-studied option: ashwagandha has by far the largest evidence base for stress, with the most consistent subjective benefit at roughly 300 to 600 mg of standardized root extract daily for 8 weeks or longer. Give it weeks, not days.
• Adaptogen blends are reasonable, with eyes open: Rhodiola, holy basil, and Schisandra combinations showed real perceived-stress benefit, but the cleanest blend trials are often run by the companies selling them. Treat a single industry study as a starting point, not a verdict.
• Match the tool to the moment: chronic background stress is a different problem from an acute spike before a presentation. Most of these trials studied weeks of daily use, not single-dose rescue, and the saffron acute-stress data is still preliminary.

What the Evidence Does Not Support

A few claims run ahead of the data. Lowering cortisol equals lowering stress. The 2025 ashwagandha meta-analysis is the direct counterexample: cortisol fell, perceived stress did not. Any adaptogen will fix burnout. These trials measured perceived stress and anxiety over weeks in generally healthy stressed adults, not clinical burnout, and effects varied by formula and by funding source. Probiotics reliably reduce stress. One strain helped a high-stress group, another missed its primary anxiety endpoint entirely. The category is promising and inconsistent, not settled.

What I Did Not Cover This Week

I focused on randomized trials and meta-analyses that paired a biological marker with a subjective stress measure. I did not cover L-theanine for acute stress (covered in the sleep edition), magnesium and the stress response in depth, omega-3s and cortisol, or lifestyle interventions like breathwork and exercise, which out-perform most supplements and deserve their own post. I also kept the saffron entry in the early-signal column rather than treating one small acute trial as a recommendation. We will return to these as the literature builds.

This article is for informational purposes and is not medical advice. Stress is individual, and persistent stress, anxiety, or burnout deserve a real conversation with a qualified professional. If you take prescription medication, have a health condition, or are pregnant or breastfeeding, talk to a healthcare practitioner before adding any supplement. Adaptogens in particular can interact with thyroid, sedative, and immune-modulating medications.

Sources

1. Albalawi AA. Dual impact of Ashwagandha: Significant cortisol reduction but no effects on perceived stress, a systematic review and meta-analysis. Nutrition and Health. 2025.
2. West RE et al. A proprietary herbal extract of ashwagandha root for stress and anxiety in healthy adults: a randomized, double-blind, three-arm, placebo-controlled efficacy and safety study. Journal of Medicine and Life. 2026.
3. McKinney E et al. Effects of multi-herb and ashwagandha root formulas on stress modulation: a randomized, double-blind, placebo-controlled clinical study. Trials. 2026.
4. Lee MC et al. Dual-Strain Psychobiotics Combining Live PS128 and Heat-Treated PS23 Improve Psychological and Neuroendocrine Outcomes in Stressed Adults: A Randomized, Placebo-Controlled Trial. Foods. 2025.
5. Day R et al. A Randomised, Double-Blind, Placebo-Controlled Trial of Probiotic and Postbiotic Strains in Healthy Adults with Self-Reported Anxiety: Effects on Mood, Vitality, Quality of Life and Perceived Stress. Brain Sciences. 2026.
6. Pouchieu C et al. Acute Effect of a Saffron Extract (Safr'Inside) and Its Main Volatile Compound on the Stress Response in Healthy Young Men: A Randomized, Double Blind, Placebo-Controlled, Crossover Study. Nutrients. 2023.

Related reading

• Cortisol Supplements
• Supplements for Stress and Anxiety

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