Ashwagandha has gone from an obscure Ayurvedic herb to one of the best-selling supplements in North America. Sales surged past $200 million annually, and social media influencers promote it for everything from anxiety relief to muscle building. But how much of the hype holds up under scientific scrutiny?
This guide examines the clinical evidence behind ashwagandha's most popular claims, explains the real risks that rarely make it into marketing materials, and helps you decide whether this ancient adaptogen deserves a place in your routine.
What Is Ashwagandha and How Does It Work?
Ashwagandha (Withania somnifera) is a small shrub native to India, the Middle East, and parts of Africa. Its root has been used in Ayurvedic medicine for over 3,000 years, traditionally classified as a "rasayana" — a rejuvenating tonic believed to promote longevity and vitality.
The plant's active compounds are called withanolides, a group of naturally occurring steroids. The most studied withanolides include withaferin A and withanolide D, which appear to modulate several biological pathways simultaneously. Modern standardized extracts typically contain between 2.5% and 10% withanolides, though the specific withanolide profile varies considerably between branded formulations.
Ashwagandha's mechanism of action is genuinely complex. Research suggests it influences the hypothalamic-pituitary-adrenal (HPA) axis, which governs your stress response. It also appears to modulate GABA receptors in the brain, interact with serotonin pathways, and exhibit antioxidant and anti-inflammatory properties. This multi-target activity is what makes ashwagandha difficult to categorize — it does not fit neatly into a single pharmacological box.
The most widely studied branded extracts include KSM-66, which uses a full-spectrum root extract, and Sensoril, which combines root and leaf extracts. These two formulations dominate clinical research and have meaningfully different withanolide profiles, making it important to distinguish between them when evaluating evidence.
Stress and Anxiety: The Strongest Evidence
The most robust clinical data for ashwagandha involves stress and anxiety reduction. A systematic review published in the Journal of Clinical Medicine analyzed multiple randomized controlled trials and found consistent reductions in perceived stress and cortisol levels among participants taking ashwagandha compared to placebo.
In one frequently cited trial, adults with chronic stress took 600 mg of KSM-66 daily for 60 days. The ashwagandha group showed a 27.9% reduction in serum cortisol levels compared to baseline, while the placebo group showed only a 7.9% reduction. Participants also reported significant improvements on validated stress questionnaires, including the Perceived Stress Scale and the Hamilton Anxiety Rating Scale.
Another double-blind study examined 60 adults experiencing moderate-to-severe anxiety. Those receiving 600 mg of a high-concentration full-spectrum extract daily for 60 days showed a 56.5% reduction in anxiety scores on the Hamilton Anxiety Rating Scale, compared to 30.5% in the placebo group. Importantly, the treatment was well-tolerated, with no serious adverse events reported.
However, context matters enormously here. Most ashwagandha anxiety studies involve small sample sizes — typically between 50 and 130 participants. The treatment durations are short, usually eight to twelve weeks. And participants generally have subclinical or mild-to-moderate anxiety rather than diagnosed anxiety disorders. This means the evidence supports ashwagandha as a complementary tool for everyday stress, not as a replacement for evidence-based treatments for clinical anxiety.
Sleep Quality Improvements
Sleep is another area where ashwagandha shows genuine promise. A meta-analysis examining five randomized controlled trials found that ashwagandha supplementation produced a small but statistically significant improvement in overall sleep quality. The effect was more pronounced in individuals with diagnosed insomnia than in those with normal sleep patterns.
The mechanism likely involves ashwagandha's GABAergic activity. Triethylene glycol, a compound found in ashwagandha leaves, has demonstrated sleep-inducing properties in animal studies. In human trials, participants taking 600 mg of ashwagandha root extract reported falling asleep faster, sleeping longer, and feeling more rested upon waking.
A 2020 study published in the Journal of Ethnopharmacology gave 150 healthy adults either 120 mg of ashwagandha extract or placebo for six weeks. The ashwagandha group showed a 72% increase in self-reported sleep quality compared to 29% in the placebo group. Actigraphy data — which tracks movement during sleep using a wristband — confirmed that participants in the supplement group spent more time in non-REM sleep.
For people struggling with stress-related sleep disruptions specifically, ashwagandha may offer particular benefit since it addresses both the upstream stress and the downstream sleep disturbance simultaneously. That said, anyone with suspected sleep apnea or other sleep disorders should pursue proper diagnosis rather than self-treating with supplements.
Testosterone and Male Reproductive Health
Ashwagandha's effects on testosterone and male fertility have generated significant interest, particularly in fitness communities. The evidence here is genuinely intriguing, though more nuanced than supplement marketing suggests.
A randomized, double-blind, placebo-controlled study gave 43 overweight men aged 40 to 70 with mild fatigue either KSM-66 or placebo for eight weeks. The ashwagandha group showed a statistically significant 14.7% greater increase in testosterone compared to placebo. Importantly, DHEA-S levels also increased, suggesting ashwagandha may influence testosterone through adrenal pathways.
Regarding fertility, a study of 46 men with low sperm count found that 675 mg of ashwagandha root extract daily for 90 days increased sperm count by 167%, improved sperm motility by 57%, and raised semen volume by 53%. A separate study of 75 infertile men showed similar improvements across multiple semen parameters.
These results are promising, but they come with significant caveats. Most testosterone studies involve small samples and short durations. The testosterone increases observed are modest — typically in the range of 10% to 22% — and occur primarily in men who are stressed, overweight, or have suboptimal baseline levels. Young, healthy men with normal testosterone are unlikely to see dramatic increases. The fertility data is more compelling but still limited to a handful of studies.
Physical Performance and Body Composition
Athletes and gym-goers represent one of ashwagandha's largest consumer demographics, and there is actually reasonable evidence supporting some performance claims.
A meta-analysis of 12 studies published in the Journal of the International Society of Sports Nutrition found that ashwagandha supplementation significantly improved VO2 max (a measure of aerobic capacity), upper and lower body strength, and recovery from exercise-induced muscle damage. The effects on VO2 max were particularly notable, with improvements ranging from 2.7% to 6.4% over control groups.
An eight-week study of 57 young men engaged in resistance training found that those taking 600 mg of KSM-66 daily gained significantly more muscle mass (measured by arm and chest circumference) and had greater increases in bench press and leg extension strength compared to the placebo group. The ashwagandha group also showed greater reductions in exercise-induced muscle damage markers and body fat percentage.
The proposed mechanisms include ashwagandha's ability to reduce cortisol (which is catabolic to muscle tissue), improve mitochondrial function, and potentially enhance creatine kinase activity during recovery. Some researchers have also hypothesized that improved sleep quality from ashwagandha indirectly supports recovery and adaptation to training.
While these findings are encouraging, most exercise studies use untrained or recreationally active participants. Whether experienced athletes training at high volumes would see similar benefits remains unclear.
Thyroid Function: Proceed With Caution
One area where ashwagandha demands particular caution is thyroid health. Multiple studies have shown that ashwagandha can increase thyroid hormone levels — both T3 and T4 — and decrease thyroid-stimulating hormone (TSH).
In a study of 50 people with subclinical hypothyroidism, 600 mg of ashwagandha root extract daily for eight weeks normalized TSH and improved T3 and T4 levels compared to placebo. For people with genuinely sluggish thyroid function who are not on medication, this could potentially be beneficial.
However, this thyroid-stimulating effect creates real risks. People with hyperthyroidism or Graves' disease should avoid ashwagandha entirely, as it could worsen their condition. Those already taking levothyroxine or other thyroid medications could experience dangerous interactions if ashwagandha pushes their levels too high. And people with normal thyroid function who take ashwagandha may develop symptoms of mild hyperthyroidism — anxiety, rapid heartbeat, weight loss, and insomnia — without realizing the supplement is the cause.
If you have any thyroid condition or are taking thyroid medication, discuss ashwagandha with your endocrinologist before starting. This is not a theoretical concern — case reports of ashwagandha-induced thyrotoxicosis have been published in medical literature.
Cognitive Function and Neuroprotection
Preliminary research suggests ashwagandha may support cognitive function, though this area needs considerably more investigation.
A small study of 50 adults found that 600 mg of ashwagandha root extract daily for eight weeks improved reaction time, attention, and working memory compared to placebo on multiple cognitive tests. Another study in adults with mild cognitive impairment showed improvements in immediate and general memory, executive function, and sustained attention after eight weeks of supplementation.
Animal studies have demonstrated that withanolides can promote neurite outgrowth, reduce amyloid beta accumulation, and protect against oxidative damage in brain tissue. These findings have generated excitement about ashwagandha's potential role in neurodegeneration prevention, but translating animal research to human clinical outcomes is notoriously unreliable.
The National Center for Complementary and Integrative Health notes that while preliminary studies show promise, current evidence is insufficient to recommend ashwagandha for cognitive enhancement or neuroprotection. More large-scale, long-term human trials are needed.
Side Effects and Safety Concerns
Ashwagandha is generally well-tolerated in studies lasting up to 12 weeks, with mild gastrointestinal discomfort being the most commonly reported side effect. However, several safety concerns deserve attention.
Liver toxicity has emerged as a serious concern. The National Institutes of Health LiverTox database documents multiple cases of clinically apparent liver injury associated with ashwagandha products. Some cases required hospitalization, and at least one required liver transplant evaluation. While these cases are rare relative to the millions of people using ashwagandha, they are severe enough to warrant monitoring.
Additional side effects and contraindications include thyroid hormone elevation (discussed above), potential interactions with immunosuppressive medications due to ashwagandha's immune-stimulating properties, possible blood sugar lowering effects that could interact with diabetes medications, and sedation that may compound the effects of benzodiazepines or other CNS depressants.
Pregnant and breastfeeding women should avoid ashwagandha, as some animal studies suggest it may have abortifacient properties at high doses. People scheduled for surgery should discontinue use at least two weeks beforehand due to potential effects on anesthesia and blood sugar control.
Dosage, Timing, and Form Selection
Clinical trials have used doses ranging from 120 mg to 1,200 mg daily, with most positive results occurring at 300 mg to 600 mg per day. The optimal dose depends partly on the extract used.
For KSM-66, most studies showing benefits used 600 mg daily, typically split into two 300 mg doses taken with meals. For Sensoril, effective doses tend to be lower — around 125 mg to 250 mg daily — due to its higher withanolide concentration from the combined root-and-leaf extraction.
Timing considerations include taking ashwagandha with food to minimize gastrointestinal side effects and improve absorption of its fat-soluble withanolides. If using it primarily for sleep, an evening dose appears most logical. For stress management, splitting the dose between morning and evening provides more consistent effects throughout the day.
Ashwagandha appears to have cumulative effects, with most studies showing benefits beginning around four to six weeks and strengthening over eight to twelve weeks. Taking it sporadically or for only a few days is unlikely to produce noticeable results.
Some practitioners recommend cycling ashwagandha — taking it for eight to twelve weeks, then stopping for two to four weeks — to prevent potential tolerance development and reduce long-term safety concerns. While no studies directly validate this approach, it is a reasonable precaution given the limited long-term safety data.
Who Should and Should Not Take Ashwagandha
Based on current evidence, ashwagandha appears most beneficial for adults experiencing chronic stress with elevated cortisol, people with stress-related sleep difficulties, men with suboptimal testosterone levels related to stress or aging, and recreationally active individuals seeking modest performance improvements.
People who should avoid ashwagandha include those with hyperthyroidism or autoimmune thyroid disease, pregnant or breastfeeding women, anyone with autoimmune conditions (due to immune-stimulating effects), people taking thyroid medications without physician supervision, those with liver disease or taking hepatotoxic medications, and anyone scheduled for surgery within two weeks.
If you decide to try ashwagandha, choose a product that uses a clinically studied extract (KSM-66 or Sensoril), is third-party tested for purity and potency, clearly states the withanolide percentage on the label, and comes from a manufacturer with good manufacturing practice (GMP) certification.
The Bottom Line
Ashwagandha is one of the more evidence-backed herbal supplements available, with genuine clinical support for stress reduction, modest sleep improvements, and potential benefits for testosterone and exercise performance. It is not, however, a miracle herb, and the science is still catching up to the marketing.
The strongest case for ashwagandha is as a complementary tool for managing chronic stress — not as a standalone treatment for clinical conditions. If you are dealing with diagnosed anxiety, depression, insomnia, or hormonal disorders, work with a healthcare provider to develop a comprehensive treatment plan rather than relying on any single supplement.
Start with a low dose, choose a reputable product, monitor for side effects (especially thyroid-related symptoms), and give it at least six weeks before evaluating results. And if you experience any unusual symptoms — particularly signs of liver distress like dark urine, yellowing skin, or upper right abdominal pain — discontinue immediately and consult your physician.
Sources and Further Reading
Health and Beyond uses reputable medical and scientific sources where possible. These links support or expand on the topics discussed above.
- systematic review published in the Journal of Clinical Medicinencbi.nlm.nih.gov
- meta-analysis of 12 studies published in the Journal of the International Society of Sports Nutritionjissn.biomedcentral.com
- National Center for Complementary and Integrative Healthnccih.nih.gov
- National Institutes of Health LiverTox databasencbi.nlm.nih.gov
