Ashwagandha vs Rhodiola: What Each Was Studied For
Key takeaways
- Ashwagandha's stress trials cluster at 300 to 600 mg of a standardized root extract a day for 8 to 12 weeks. The most cited one gave 64 chronically stressed adults 300 mg twice daily for 60 days.
- Rhodiola's trials run lower and shorter. The best known gave 60 adults with stress-related fatigue 576 mg of the SHR-5 extract for 28 days.
- The trials behind both herbs randomized between 10 and 103 people. A systematic review of 11 controlled rhodiola studies rated every one at high or unclear risk of bias.
- No published trial has randomized ashwagandha against rhodiola head to head. A 2026 four-arm study gave the pair together to 103 adults for 14 days, paid for by the supplement manufacturer, and included no arm using either herb alone.
- The two were studied against different endpoints, so "which one works better" is a question the literature never asked.
What ashwagandha was studied for
Chandrasekhar and colleagues enrolled 64 adults with a history of chronic stress and randomized them to 300 mg of a full-spectrum root extract twice daily or placebo for 60 days. Perceived Stress Scale scores fell 44.0% against 5.5% on placebo, and serum cortisol fell further in the treated group, with a p value of 0.0006 for the between-group comparison. The paper declared no conflicts of interest, which is unusual here. A second trial, in 57 young men new to weight training, used the same 600 mg daily dose for 8 weeks and reported larger bench press gains and a bigger fall in exercise-related cortisol. That one was supplied by the extract's manufacturer.
Neither trial measured anxiety as a clinician would. Both leaned on questionnaires the participants filled in themselves.
What rhodiola was studied for
Olsson and colleagues took 60 people aged 20 to 55 who met Swedish diagnostic criteria for fatigue syndrome and gave half of them four tablets a day of the SHR-5 extract, 576 mg in total, for 28 days. Both groups improved on the burnout scale. The treated group improved more, and the authors also reported a difference in the cortisol response to waking. Twenty-eight days is short for a condition defined by months of exhaustion, and the trial was run by researchers with ties to the extract's manufacturer.
The other commonly cited rhodiola trial is smaller still. Ten adults with generalized anxiety disorder took 340 mg a day for 10 weeks in an open-label pilot with no placebo arm. A 12-week, three-arm trial in 57 adults with mild to moderate depression compared rhodiola, sertraline, and placebo. Rhodiola beat placebo by a margin that didn't reach significance on the primary scale, and sertraline did better. Thirty percent of the rhodiola arm reported adverse events against 63.2% on sertraline.
The sample size problem
Add up the trials cited above and the range is 10 to 103 participants. That's enough to detect a shift in a questionnaire score. It isn't enough to detect an uncommon harm. Ishaque and colleagues reviewed 11 controlled studies of rhodiola for physical and mental fatigue and found the results contradictory: 2 of 6 trials in healthy people reported a physical performance benefit, and 3 of 5 reported a mental fatigue benefit. Every study carried a high or unclear risk of bias. The authors' conclusion was that a properly designed trial was still needed.
Twenty years later, that sentence still applies to most of this shelf.
Ashwagandha has more trials and a similar problem. Doses vary between 120 and 600 mg, extracts are standardized to different withanolide percentages, and the same brand name appears in a large share of the positive papers.
The head-to-head gap
I looked for a trial that randomized one herb against the other and found none. What exists is a 2026 study from a University of South Carolina group that randomized 103 physically active adults to four arms: both supplements, morning only, evening only, or placebo. The morning capsule contained 600 mg of ashwagandha plus 300 mg of rhodiola. The study ran 14 days, and the company that made the products funded it.
The morning arm reported lower perceived stress and better subjective sleep quality. No arm tested ashwagandha alone or rhodiola alone, so the trial can't separate the two, and 14 days is a short window for either.
That leaves every comparison you'll read online as a comparison of two separate literatures, not of two treatments.
Doses and extracts don't travel
A milligram is not a milligram here. KSM-66 is a root-only extract standardized to 5% withanolides. Sensoril comes from root and leaf and carries a different withanolide content. The trials used specific branded extracts, and a generic root powder at the same milligram dose is a different product.
Rhodiola has the same issue. SHR-5 is standardized to 3% rosavins and 1% salidroside. The EMA monograph covers dry extracts at 144 to 400 mg a day for traditional use, which is a regulatory category, not an efficacy finding.
Safety looks different too
Ashwagandha carries a liver signal that rhodiola doesn't. The NIH LiverTox database has an entry describing cholestatic injury appearing 2 to 12 weeks after people start the herb, usually resolving after they stop.
Denmark's food authority concluded in 2023 that a safe intake level for ashwagandha extracts could not be set. The EMA reached a similar place in 2024, and Australia's regulator issued a liver warning.
Rhodiola's regulatory story runs the other way. The EMA grants traditional use for stress symptoms such as fatigue, while stating that clinical evidence of efficacy is insufficient. That's a recognition of long use, not a verdict on the trials.
Both herbs are plausible interaction candidates with psychiatric medication.
Frequently asked questions
Can you take ashwagandha and rhodiola together?
People do, and the 2026 four-arm trial tested exactly that combination at 600 mg plus 300 mg for 14 days. One small trial doesn't establish much, and it was funded by the manufacturer.
Which one is better for anxiety?
Ashwagandha has more trials with anxiety scales as an endpoint, and rhodiola's anxiety evidence rests largely on a 10-person pilot. More trials isn't the same as better trials, though.
Does rhodiola keep you awake?
It's described as stimulating in traditional use and is usually taken in the morning. The trials don't offer a clean answer on sleep onset, and one small study reported worse fatigue scores on rhodiola.
Are these safe to take long term?
Nobody has run a trial long enough to answer that for either. Ashwagandha has a documented liver signal and a regulatory caution in Europe. Rhodiola's long-term data is thin in a different way.
Is either a substitute for a prescribed treatment?
No. Neither has been tested against a first-line treatment in an adequately powered trial, and the one three-arm comparison in depression found rhodiola behind sertraline.
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This article is for general information only and does not constitute medical advice. Statements about dietary supplements have not been evaluated by the Food and Drug Administration and are not intended to diagnose, treat, cure, or prevent any disease. Talk with your health care provider before using ashwagandha or rhodiola, especially if you take prescription medication.
Sources
- Chandrasekhar K et al., A prospective, randomized double-blind, placebo-controlled study of a high-concentration full-spectrum extract of ashwagandha root, Indian J Psychol Med 2012
- Olsson EM et al., A randomised, double-blind, placebo-controlled study of the standardised extract SHR-5 of Rhodiola rosea in subjects with stress-related fatigue, Planta Med 2009
- Mao JJ et al., Rhodiola rosea versus sertraline for major depressive disorder: a randomized placebo-controlled trial, Phytomedicine 2015
- Ishaque S et al., Rhodiola rosea for physical and mental fatigue: a systematic review, BMC Complement Altern Med 2012
- NIH LiverTox, Ashwagandha clinical and research information on drug-induced liver injury
- European Medicines Agency, European Union herbal monograph on Rhodiola rosea L., rhizoma et radix, revision 2024