Ashwagandha for Strength Training: What This 8-Week Study Really Showed (and What It Means for Your Stack)
Summary
If you've seen Ashwagandha marketed as a "natural testosterone booster" or muscle-building adaptogen and wondered whether the hype holds up, this 2024 study is one of the better pieces of evidence you'll find — and it's notable for including women, who are almost always left out of this research.
Researchers in India ran an 8-week, randomized, double-blind, placebo-controlled trial on 80 healthy, already gym-active adults (ages 18-45, both sexes) who were already lifting regularly. Half took 600 mg/day of KSM-66 (a standardized, high-concentration Ashwagandha root extract with over 5% withanolides, split into two 300 mg doses), and half took an identical-looking placebo capsule. Everyone followed the same structured resistance-training program, three days a week, for eight weeks. Seventy-three participants (37 Ashwagandha, 36 placebo) completed the study with usable data — a small number dropped out due to simple forgetfulness, not side effects.
The results favored Ashwagandha across the board. On the primary measures — 1-rep-max bench press and leg press — the Ashwagandha group improved significantly more than placebo in both men and women (bench press up ~23% within the AG group vs. much smaller placebo gains; leg press up 15% in men and ~10% in women). Cardiorespiratory endurance (VO2max, measured via a treadmill test) rose about 9.5% in men and 7% in women taking Ashwagandha — notably outpacing placebo. Muscle girth also grew more with Ashwagandha at the chest and upper arm, though thigh circumference gains weren't statistically different from placebo. Effect sizes were large (Cohen's d around 1.0-1.5), which is a bigger signal than you typically see in supplement trials.
This isn't an isolated result. It builds on earlier work — Wankhede et al. (2012) found similar strength gains with 600 mg/day in untrained men, and a 2021 Bayesian meta-analysis (Bonilla et al.) pooling multiple Ashwagandha trials found a smaller but still positive effect on physical performance. More recent meta-analyses (2024-2025) estimate Ashwagandha raises VO2max by roughly 3 ml/kg/min on average across studies — consistent with what this trial found. A newer 57-person trial in untrained men reported even larger bench press gains (46 kg vs 26.4 kg for placebo), and 2025 research has started extending this work specifically to female athletes' recovery, addressing exactly the sex-data gap this study was designed to fill.
Safety-wise, this trial reported zero adverse events and no meaningful changes in blood work (liver, kidney, thyroid, hematology) over 8 weeks — reinforcing Ashwagandha's reputation as one of the better-tolerated herbal supplements on the market.
What This Means For You
Dosage and timing: This trial used 600 mg/day of KSM-66 specifically (300 mg twice daily, cellulose capsules, taken with milk or water), for 8 weeks alongside structured resistance training. That's the dose with the most direct trial support here — not the 250 mg or "as needed" doses common in stress/sleep-focused ashwagandha products. If you're buying a product to mirror this study, look specifically for "KSM-66" or another standardized extract stating ">5% withanolides" on the label — generic, non-standardized ashwagandha powder wasn't tested and may not deliver comparable results.
Who benefits most: Participants here were already resistance-training for 3+ months, so this isn't a substitute for training — it's an adjunct. The gains appeared on top of a structured program, not instead of one. Both men and women saw meaningful strength and endurance improvements, which is reassuring given most older ashwagandha research studied men only.
What to expect: Don't expect steroid-like transformations. The upper-body/lower-body strength gains and VO2max improvements were statistically robust, but chest/arm girth increases were modest, and thigh circumference and body fat showed no significant advantage over placebo — the study wasn't even powered to detect body-composition changes.
Cost-benefit: Ashwagandha extract is inexpensive relative to many "performance" supplements (creatine, protein aside), and the safety profile here (zero adverse events, stable labs) is favorable for an 8-week course. Reasonable candidates: recreational or intermediate lifters wanting an incremental edge in strength and cardio capacity. People on blood pressure medication, thyroid conditions, hormone-sensitive conditions, or who are pregnant should talk to a doctor first, since ashwagandha can affect thyroid hormones and blood pressure in some people even though this trial didn't detect such effects.
Important Considerations
This was a well-conducted trial (Jadad score 5/5, the maximum), but a few limits matter. First, participants were young-to-middle-aged (18-45), already resistance-trained, and recruited from gyms in India — results in older adults, complete beginners, or people with health conditions weren't tested. Second, the trial only ran 8 weeks; whether gains continue, plateau, or reverse with longer or shorter use is unknown. Third, diet wasn't tracked quantitatively — participants self-reported following their usual diet, so nutrition differences between groups can't be fully ruled out as a contributing factor. Fourth, seven participants (about 9%) were excluded from the efficacy analysis due to non-compliance, which wasn't anticipated in the original study design and could subtly affect results, though the effect sizes were large enough that this is unlikely to change the overall conclusion. Fifth, the study was funded by and used extract supplied by Ixoreal BioMed, the maker of KSM-66 — a common arrangement in supplement research, but one that carries an inherent conflict-of-interest to weigh alongside the results. Finally, results with generic or lower-concentration ashwagandha products may differ, since only the specific standardized KSM-66 extract at 600 mg/day was tested. As with any supplement, check with a healthcare provider before starting, especially if you take thyroid, blood pressure, sedative, or hormone-related medications, or are pregnant or breastfeeding — none of which were included in this trial population.
Terms Explained
Technical Study Details
Study Design
Total Score
JADAD Quality Assessment評価詳細
Randomization
2 / 2Blinding
2 / 2Dropouts/Withdrawals
1 / 1Study Population
- Healthy adults of either sex aged 18-45 years
- Engaging in regular physical activity (gymnasium/strength training) for at least three months before screening
- Willing to sign informed consent
- Agreed to follow same exercise schedule and diet regime for study period
- If of child-bearing age, agreed to use barrier birth control measures
Interventions
Ashwagandha (KSM-66) standardized root extract
TreatmentPlacebo (starch)
ControlOutcomes
| Outcome | Type | Effect | p-value |
|---|---|---|---|
| 1 Repetition Maximum (1RM) Bench Press | Primary | 1.14 | <0.0001Significant |
| 1 Repetition Maximum (1RM) Leg Press | Primary | 1.11 | 0.0005Significant |
| Mid-upper arm circumference (muscle girth) | Secondary | - | <0.0001Significant |
| Chest circumference (muscle girth) | Secondary | - | 0.019Significant |
| Upper thigh circumference (muscle girth) | Secondary | - | - |
| Cardiorespiratory endurance (VO2max) | Secondary | 1.03 | <0.0001Significant |
| Adverse events | Secondary | - | - |
Safety
Conclusion
Eight weeks of Ashwagandha (KSM-66) root extract supplementation (600 mg/day) combined with resistance training significantly improved muscle strength (1RM bench press and leg press), muscle size (arm and chest circumference), and cardiorespiratory endurance (VO2max) compared to placebo in both male and female participants, with no adverse events reported, suggesting it could be a safe, effective, low-cost supplement for athletes.Limitations
- Unanticipated data loss due to poor compliance (not lost to follow-up) that was not accounted for in the sample size calculation or study planning
- Lack of quantitative data on subjects' food intake (calorie and protein consumption), relying only on self-reported adherence via subject diaries
- Some participants in both groups consumed capsules with milk, and the study could not establish the effect of milk consumption on study parameters
- Study focused only on resistance-trained adults over a short 8-week duration, so extrapolation to other populations or longer durations should be done with caution
- Study was not adequately powered to assess changes in body fat/body composition