By the Thursday of a stretched week, a familiar state sets in: worn out but unable to switch off, running on caffeine and short sleep. That tired-but-wired feeling is what sends a lot of people looking at adaptogens, the botanicals sold as a way to help the body cope with stress. Two fair questions follow. Do they actually do anything, and if so, which one is worth trying?
Here is what the human research supports for the three you are most likely to meet, which people it studied, and where it runs out.
Do adaptogens actually help with stress?
"Adaptogen" is a research-and-marketing category for botanicals studied in relation to the body's stress response. It is not a defined mechanism, dose or clinical result. That matters when you read a claim, because trials in this area measure different things: serum cortisol, a perceived-stress questionnaire, sleep scores, task performance. Those endpoints are related but they are not interchangeable, and a drop in a cortisol reading does not automatically mean the people in the study felt calmer.
So the useful version of the question is narrower. For a given botanical, is there human evidence, in people whose situation resembles yours, that something measurable changed? For most adaptogens that evidence is thin. For one it is better than the rest.
Which adaptogen has the most human evidence?
Ashwagandha (Withania somnifera), and it is not close. A 2024 systematic review pooled nine trials of varied ashwagandha preparations and reported differences from placebo in perceived-stress scores, anxiety scales and serum cortisol, alongside substantial variation across preparations and methods 2. A 2025 meta-analysis drew a tighter line: across its pooled studies it found a cortisol reduction but no significant pooled change in perceived stress 3. Read together, the cortisol signal is reasonably consistent; whether participants felt different is the less settled part.
Who were those trials in? Mostly adults under ordinary stress, often recruited during demanding stretches of work or study, taking a standardised extract for a short run of weeks. That places ashwagandha as more relevant to people whose situation matches the studied group than as a general tonic for anyone.
The cautions are worth reading too. The US National Institutes of Health notes trials have used root-only and root-and-leaf extracts across a wide dose range, that the study base is small, and that most trials are short, so safety beyond the studied periods is less certain 1. It also flags potential medicine interactions and cautions around pregnancy, breastfeeding, thyroid function and reported cases of liver injury.
How the label compares with the trials
Pure Encapsulations Ashwagandha provides 500 mg of root extract per capsule, standardised to 2.5% withanolides, which works out to 12.5 mg of declared withanolides. The direction is one capsule daily, with or between meals. It is a short formula: the rest is plant fibre and a cellulose capsule.
One thing to know before you match a label to a headline result. A root-only extract is not interchangeable with the proprietary root-and-leaf extracts several trials used, because plant part, extract weight and marker content all differ between products. The 60-capsule bottle gives you 60 daily servings at the labelled dose. How any one person responds is a separate question the label cannot answer.
What about passionflower?
Passionflower (Passiflora incarnata) shows up in New Zealand stress formulas, though it is not usually counted as a traditional adaptogen. Its evidence is thinner and tied to specific preparations. A 2020 systematic review found nine varied clinical trials, most reporting a direction of effect on an anxiety measure, but the preparations, comparators and durations differed too much to generalise from 5. A 2024 randomised trial tested one aerial-parts extract at bedtime for 30 days in 65 participants with stress and sleep complaints 6.
Much of the remaining evidence is laboratory work. A 2011 study found the extract acted on GABA uptake and on GABA-A and GABA-B receptors in a dish, without touching the benzodiazepine site 4. That kind of lab activity is a lead, not a clinical outcome.
The practical catch is the finished product. Metagenics NeuroCalm pairs passionflower with three other botanicals (zizyphus, kudzu and magnolia) and directs one tablet three times daily, not a single evening dose. A four-herb blend on that schedule has not itself been trialled, so the passionflower studies do not transfer to it. Read it as its own product, and check the delivered label, since the extract amounts differ across the 30-, 60- and 120-tablet panels.
And rhodiola?
Rhodiola rosea has the least to stand on of the three. A 2012 systematic review of 11 controlled studies of physical or mental fatigue found mixed results, with only two of six trials in healthy people showing a physical-fatigue benefit, and judged every included study to carry a high risk of bias or reporting problems 7. That is too uneven to build a confident recommendation on, which is why we do not currently carry a rhodiola-only product.
So, which one, if any?
| Botanical | Human evidence | Studied in | In our range |
|---|---|---|---|
| Ashwagandha | Broadest here; cortisol signal fairly consistent, felt-stress less so | Adults under everyday work or study stress, short courses | Pure Encapsulations Ashwagandha |
| Passionflower | Small and preparation-specific | Varied trials on anxiety and sleep measures | Part of NeuroCalm (untested as a blend) |
| Rhodiola | Weakest; high risk of bias across studies | Physical and mental fatigue, uneven results | Not currently stocked |
If you are going to try one, ashwagandha is the reasonable pick, and it fits best when your stretched week resembles the trials: everyday pressure over a defined period, rather than a crisis or a long-standing condition. Passionflower is worth understanding if you are weighing a formula like NeuroCalm, though the blend's own research does not back it. Rhodiola is the thinnest of the three.
None of this is a substitute for the basics. Sleep timing, movement, food and caffeine do more for a stressed week than any capsule. A supplement earns a place only with a defined reason, one change at a time, and a point where you check whether the thing you were tracking actually shifted.
Our Stress and Sleep collection has the current range, and the Stress and Sleep Guide covers the wider category and where products overlap. If you take medicines, are pregnant or breastfeeding, or have a health condition, read the delivered label and speak to a qualified healthcare professional first.
This article is for general educational purposes only. It is not medical advice, and nothing here is intended to diagnose, treat, cure, or prevent any disease. Always read the label and use as directed.
References
- National Institutes of Health Office of Dietary Supplements. Ashwagandha: Is it helpful for stress, anxiety, or sleep? Health Professional Fact Sheet. Updated 2 May 2025. https://ods.od.nih.gov/factsheets/Ashwagandha-HealthProfessional/
- Arumugam V, Vijayakumar V, Balakrishnan A, et al. Effects of Ashwagandha (Withania somnifera) on stress and anxiety: a systematic review and meta-analysis. Explore. 2024;20(6):103062. doi:10.1016/j.explore.2024.103062 (PMID: 39348746)
- Albalawi AA. Dual impact of Ashwagandha: significant cortisol reduction but no effects on perceived stress. Nutrition and Health. 2025;31(4):1395-1408. doi:10.1177/02601060251363647 (PMID: 40746175)
- Appel K, Rose T, Fiebich B, et al. Modulation of the gamma-aminobutyric acid (GABA) system by Passiflora incarnata L. Phytotherapy Research. 2011;25(6):838-843. doi:10.1002/ptr.3352 (PMID: 21089181)
- Janda K, Wojtkowska K, Jakubczyk K, et al. Passiflora incarnata in neuropsychiatric disorders: a systematic review. Nutrients. 2020;12(12):3894. doi:10.3390/nu12123894 (PMID: 33352740)
- Harit MK, Mundhe N, Tamoli S, et al. Randomized, double-blind, placebo-controlled clinical study of Passiflora incarnata in participants with stress and sleep problems. Cureus. 2024;16(3):e56530. doi:10.7759/cureus.56530 (PMID: 38646244)
- Ishaque S, Shamseer L, Bukutu C, Vohra S. Rhodiola rosea for physical and mental fatigue: a systematic review. BMC Complementary and Alternative Medicine. 2012;12:70. doi:10.1186/1472-6882-12-70 (PMID: 22643043)