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Ashwagandha gives workouts only a small, shaky boost, review finds
A systematic review in the journal Nutrients pooled 13 randomized trials in about 599 people and found ashwagandha gave exercise performance only a small, unreliable lift.
Based on a peer-reviewed study in Nutrients
- A systematic review and three-level meta-analysis in the journal Nutrients pooled 13 randomized controlled trials of ashwagandha for exercise performance, covering about 599 participants.
- On average ashwagandha edged out a placebo, but the benefit was small and unreliable: the standardized effect was about 0.47 (Hedges' g, where 0.2 is small and 0.5 is moderate), and the prediction interval crossed zero, meaning it might do little or nothing for a given person.
- The signal was clearest for aerobic endurance; for strength it was positive but uncertain, and for power or muscular endurance the evidence was too thin to judge.
- The trials were small and varied, and most participants were young adults or athletes, not older or general-population people, so the results may not carry over.
- The most evidence-supported dose was about 500 to 600 milligrams of extract a day. Ashwagandha is a supplement and is not tightly regulated, so anyone on medication or who is pregnant should check with a clinician first.
Ashwagandha, an herb long marketed to calm stress, has picked up a second job: workout aid. Bottles now promise more stamina and bigger gains.
Whether it delivers has been an open question, tested only in scattered, small studies. A new analysis in the journal Nutrients gathered them, and on average ashwagandha improved overall exercise performance, though the lift was small and shakier than a single number suggests.
Adding up thirteen trials
Until now, ashwagandha’s workout studies had been small and one-off, easy to wave away in either direction. The new review, published in the journal Nutrients, pooled thirteen trials involving 599 participants to gauge both the size of the benefit and how far it can be trusted.
Every study it drew on was a randomized controlled trial: some people were given oral ashwagandha, with placebo or a control for comparison, so a genuine effect could be told apart from a hopeful guess. A meta-analysis like this one stacks many separate trials together to find the overall picture, which carries more weight than any lone result.
One at a time, these studies were small, and they span heterogeneous performance domains, which is to say they tested very different kinds of exercise, from short sprints to long-distance efforts.
A small nudge, clearest for endurance
The gains were not spread evenly across the board. Evidence was most consistent for aerobic endurance, the staying power that carries you through a run or a long ride.
For raw strength, the effects were positive but uncertain. Power or muscular endurance, the explosive and sustained kinds of effort, had too little evidence to call.
On dose, the trials pointed to roughly 500 to 600 milligrams of extract a day as the most evidence-supported range, though the researchers treat the dose question as unsettled, more a hint than a firm guide.
Why the average may not travel
The average is only half the story. The researchers also gauged how reliable the benefit would be in a new setting, beyond the typical result past trials produced. That reliability check, called a prediction interval, crossed zero, which means the true effect in a fresh group could be a worthwhile boost or close to nothing.
It matters, too, who was studied. Samples were mainly young adults or athletes, a group some distance from the older or sedentary people who most often reach for a bottle.
The authors are blunt about the fixes the field needs: future studies, they write, should be preregistered, adequately powered, double-blind and run on a standardized formula, so results are not tilted by expectation. Registered plans, enough participants, and blinding so neither side knows who took the real supplement: the trials so far often fell short of that.
Two practical notes sit underneath all this. Ashwagandha is sold as a dietary supplement, which means it is not screened for safety and effectiveness the way a prescription drug is, and the amount in a capsule can differ between products. Because it is biologically active, anyone taking regular medication, or who is pregnant or breastfeeding, should run it past a doctor first.
Still, this is not a thumbs-down. The authors conclude that oral ashwagandha “may improve selected exercise-performance outcomes, particularly aerobic endurance, but benefits are not uniform across contexts.”
The honest read is a small maybe: possibly a modest lift for endurance, and nothing you should count on.
People also ask
Should I take ashwagandha to work out harder?
The honest answer is that the evidence is thin. Pooled across 13 small trials, ashwagandha showed a small average benefit for exercise, but it was unreliable, so it might help you a little or not at all. If you want to try it, treat it as a low-confidence experiment and keep your expectations modest. If you take any medication, or are pregnant or breastfeeding, ask a doctor first.
How strong was the effect?
Modest. The average was a standardized effect of about 0.47 (Hedges' g), which counts as small to moderate. But the 95 percent prediction interval ran from roughly -0.4 to 1.3, and because it crossed zero, the benefit is not dependable in a new person or setting. The clearest signal was for aerobic endurance; strength was positive but uncertain.
What is a prediction interval, and why does it matter here?
It estimates how much the effect might vary the next time the supplement is tested in a fresh group, rather than only reporting the average from past trials. A wide interval that crosses zero, as here, means the true effect in a new setting could be a worthwhile benefit or essentially nothing. It is a stricter, more honest test than the average alone.
Is ashwagandha safe to take?
The trials generally used about 500 to 600 milligrams of extract a day, but the review did not focus on safety and long-term data are limited. Ashwagandha is sold as a dietary supplement, so it is not screened as strictly as a prescription drug, and the amount in a product can vary. People who take any medication, or who are pregnant or breastfeeding, should check with a clinician before using it.