What Are the Benefits of Ashwagandha?

Ashwagandha, a shrub native to India and parts of Africa, has the strongest clinical backing for reducing stress and anxiety, with consistent trial results showing it lowers the stress hormone cortisol and improves scores on standardized anxiety scales. But the list of studied benefits extends well beyond stress relief into sleep, physical performance, cognition, reproductive health, and blood sugar regulation, with varying degrees of evidence behind each claim. The plant has been used in Ayurvedic medicine for centuries as a general tonic, and modern research has been catching up to many of those traditional uses with controlled trials.

Stress and Anxiety Relief

This is the area where ashwagandha has the deepest evidence base and where most people first encounter the supplement. A dose-response meta-analysis of randomized controlled trials found that ashwagandha significantly improved stress, depression, and anxiety scores compared to placebo across multiple studies.¹ A separate meta-analysis focused on people with diagnosed mental health conditions found similar patterns, with meaningful reductions in anxiety, depression, and stress symptoms, though the authors noted substantial variability between studies.²

One of the more compelling individual trials gave participants either 600 mg of ashwagandha extract or a placebo daily for eight weeks and measured morning cortisol. The ashwagandha group saw roughly a 23% drop in cortisol levels, while the placebo group barely changed. Anxiety scores on a standard clinical scale also improved significantly in the supplement group.³ The cortisol reduction is a recurring finding across trials and is one reason researchers classify ashwagandha as an “adaptogen,” a substance that helps the body manage physiological stress responses.

Worth noting: most stress and anxiety trials use standardized root extracts at doses between 300 and 600 mg per day, taken for at least six to eight weeks. The benefits tend to be moderate rather than dramatic. If you are dealing with clinical anxiety or a diagnosed mood disorder, ashwagandha is not a substitute for professional treatment, but it may be a useful complement.

Sleep Quality

The connection between stress reduction and better sleep is intuitive, and the trial data on ashwagandha and sleep bears it out. A study in healthy adults found that six weeks of ashwagandha supplementation significantly improved sleep efficiency, total sleep time, and the time it took to fall asleep, all measured with activity-monitoring devices rather than just self-reports.⁴

A separate trial looked at both healthy volunteers and people with insomnia and found improvements across both groups, though the effects were more pronounced in the insomnia group. Sleep onset latency, or how long it took to fall asleep, and sleep efficiency were the parameters that improved the most. The insomnia group also reported better mental alertness during the day.⁵ The meta-analysis of people with mental disorders also reported improved sleep quality as a secondary outcome.²

If you are considering ashwagandha specifically for sleep, the evidence suggests it works best for people who have trouble falling asleep or staying asleep due to stress or anxiety, rather than for sleep disorders with other root causes.

Physical Performance and Strength

Ashwagandha has attracted serious interest in the fitness world, and the research here is surprisingly robust. A systematic review and Bayesian meta-analysis found that supplementation improved variables related to physical performance in both men and women compared to placebo.⁶

The cardiorespiratory fitness angle is well-studied. A meta-analysis of trials measuring VO2max, the gold standard for aerobic capacity, found a statistically significant improvement in both athletes and non-athletes taking ashwagandha.⁷ A trial in elite Indian cyclists showed significant improvements in VO2max, metabolic equivalents, and time to exhaustion after eight weeks, while the placebo group saw no change.⁸ Another trial in healthy athletic adults using a standardized root extract found that VO2max increased substantially more in the ashwagandha group than in the placebo group at both eight and twelve weeks.⁹

On the strength side, a controlled trial in young men doing resistance training found that the ashwagandha group gained significantly more muscle strength on the bench press and leg extension, had greater increases in arm and chest muscle size, lost more body fat, and had a greater increase in testosterone levels compared to the placebo group. They also showed signs of less exercise-induced muscle damage.¹⁰ These are not subtle differences. The bench press strength gain was roughly 46 kg in the ashwagandha group compared to about 26 kg in the placebo group over the study period.

The practical upshot for gym-goers and athletes: ashwagandha appears to support both endurance and strength adaptations to training. It is not going to replace proper programming and nutrition, but the magnitude of the effects in several trials is large enough to be practically meaningful rather than just statistically detectable.

Cognitive Function

A smaller but growing body of evidence suggests ashwagandha can sharpen certain aspects of mental performance. A trial testing the effects of a single dose found that ashwagandha improved working memory on increasingly demanding tasks and helped sustain attention by preventing the reaction-time slowdown that typically comes with mental fatigue.¹¹ This is interesting because most supplement trials look at chronic use; finding acute effects suggests a relatively fast mechanism of action on cognition.

A study that tested both acute and 30-day supplementation found improvements in word recall, choice reaction time, picture recognition, and digit vigilance. The researchers also measured mood and found that tension and fatigue improved.¹² The cognitive benefits likely tie back to the stress-reduction mechanism. When your cortisol levels are chronically elevated, memory and attention suffer. Bringing cortisol down tends to improve cognitive performance as a downstream effect.

The evidence here is promising but still early-stage compared to the stress and exercise research. Most cognitive trials have been small, and it remains unclear whether the improvements would show up in people who are already cognitively sharp versus those experiencing stress-related mental fog.

Reproductive and Sexual Health

Ashwagandha has been studied in both men and women for reproductive health, and the findings are notable in both cases. In men with low sperm counts, a pilot study found that 90 days of ashwagandha root extract produced a 167% increase in sperm concentration, a 53% increase in semen volume, and a 57% increase in sperm motility. Serum testosterone also rose by about 17%.¹³ A review of the broader literature on ashwagandha and male infertility confirmed that it can improve sperm count and motility while regulating reproductive hormones.¹⁴

For women, a pilot study measured sexual function using validated clinical scales and found that ashwagandha significantly improved arousal, lubrication, orgasm, satisfaction, and the total number of successful sexual encounters compared to placebo.¹⁵ Sexual distress scores also dropped significantly.

Both the male fertility and female sexual function studies are pilot-scale, meaning they used small sample sizes. The results are encouraging and the effect sizes are large, but larger confirmatory trials are still needed before drawing strong conclusions. The testosterone increases seen in men, while statistically significant, have also appeared in the exercise trials, suggesting ashwagandha may have a real but modest effect on testosterone across different contexts.

Blood Sugar and Metabolic Health

There has been growing interest in ashwagandha’s effects on blood sugar regulation, particularly for people with or at risk for type 2 diabetes. A recent dose-response meta-analysis of 15 randomized controlled trials found that ashwagandha modestly reduced fasting blood glucose by about 3 mg/dL compared to placebo. However, the effect on HbA1c, which reflects longer-term blood sugar control, was inconclusive, and the overall certainty of the evidence was rated very low.¹⁶

The mechanistic picture is more intriguing than the clinical trial results so far. Research suggests ashwagandha’s active compounds, called withanolides, may improve insulin sensitivity and help regulate glucose through several pathways, including effects on enzymes involved in carbohydrate digestion and pancreatic insulin secretion.¹⁷ A review of the broader evidence noted that while animal studies show clear blood-sugar-lowering effects, human clinical evidence remains limited.¹⁸

The honest read here: ashwagandha is not a diabetes treatment. A 3 mg/dL reduction in fasting blood glucose is real but clinically tiny. It may offer a marginal benefit as part of a broader metabolic health strategy, but anyone managing diabetes should rely on established therapies and not expect ashwagandha to move the needle in a meaningful way.

Thyroid Function

One of the more specific and sometimes overlooked uses of ashwagandha is in supporting thyroid function, particularly in people with subclinical hypothyroidism, a condition where thyroid levels are slightly off but not low enough for a full hypothyroidism diagnosis. A double-blind trial of subclinical hypothyroid patients found that eight weeks of ashwagandha root extract significantly improved TSH, T3, and T4 levels compared to placebo, effectively normalizing thyroid indices over the treatment period.¹⁹

Animal research has also supported the thyroid connection, with one study in hypothyroid rats finding that ashwagandha extract improved thyroid hormone levels and reduced oxidative stress in the thyroid gland.²⁰

This is important to flag because it cuts both ways. If you have an underactive thyroid or subclinical hypothyroidism, ashwagandha might genuinely help. But if you are already on thyroid medication, ashwagandha could push your levels too high or interfere with dosing. Anyone on levothyroxine or similar medications should talk to their doctor before adding ashwagandha to the mix. And if you have hyperthyroidism or Graves’ disease, ashwagandha is a bad idea since stimulating thyroid function is the opposite of what you need.

Inflammation Markers

A systematic review of ashwagandha’s effects in healthy adults found that supplementation reduced creatine kinase and C-reactive protein levels, both markers of inflammation, compared to controls. The authors noted that this reduction occurred even in individuals who started with low baseline inflammation, suggesting a general anti-inflammatory effect rather than one limited to people with existing conditions.²¹ This finding is consistent with ashwagandha’s traditional classification as a Rasayana, or rejuvenating tonic, in Ayurvedic medicine, where it has been used for centuries to promote general vitality and resilience.²²

Chronic low-grade inflammation is linked to a wide range of health problems over time, so a supplement that modestly lowers inflammatory markers in otherwise healthy people is potentially useful for long-term wellness even if the effects are not dramatic in the short term.

Safety Concerns and Liver Risk

Ashwagandha is generally well-tolerated at standard doses in trials lasting up to 12 weeks, and serious adverse events in published studies are rare. But there is a growing concern that deserves attention: liver injury. Case reports of ashwagandha-related liver damage have come from multiple countries. In one reported case, a man who had been taking ashwagandha for a year developed jaundice, with elevated liver enzymes and bilirubin. He required intensive treatment including multiple plasmapheresis sessions.²³

A review cataloguing all reported cases added two new ones: a 36-year-old man who developed nausea, itching, and dark urine after six months of taking 450 mg three times daily, and a 30-year-old woman who developed similar symptoms after just 45 days on the same dose. Both had elevated liver enzymes, and both improved after stopping the supplement. Using a standard causality assessment tool, the relationship to ashwagandha was rated as “probable” in both cases. At least one other documented case ended in liver transplantation.²⁴

The absolute risk appears to be low given the millions of people taking ashwagandha worldwide, but the severity of the cases is concerning. If you use ashwagandha regularly, symptoms like yellowing of the skin or eyes, dark urine, unusual fatigue, or upper abdominal pain should prompt you to stop the supplement and see a doctor. People with pre-existing liver conditions should be especially cautious.

Supplement Quality Is a Serious Problem

Even if ashwagandha itself is safe and effective, the supplement in your cabinet might not contain what the label says. A recent comparison of commercial ashwagandha products against British and US pharmacopoeia quality standards found alarming failure rates: over 44% of tested products failed British standards and 60% failed US standards. Of 25 products tested, only 10 met both sets of standards. Just two were confirmed to contain root-only material as traditionally used. The rest contained varying proportions of aerial parts, such as leaves and stems, which have different chemical profiles and are not what most clinical trials use.²⁵

This matters because the active compounds in ashwagandha, the withanolides, vary significantly between root and aerial parts. Withaferin A, for example, is found at higher concentrations in leaves and has different biological activity than the compounds concentrated in roots. Most clinical trials demonstrating benefits used standardized root extracts, so a product containing undisclosed leaf material may not produce the same effects and could introduce different safety profiles.²⁶

If you are buying ashwagandha, look for products that specify “root extract” and ideally list a standardized withanolide content. Branded extracts like KSM-66 and Sensoril are the formulations most commonly used in published trials, which at least means there is data behind what you are taking. Third-party testing certifications can also help, though they address contamination more than plant-part sourcing. The broader supplement industry remains poorly regulated, and ashwagandha is no exception to that pattern.