If you’ve heard about ashwagandha in recent years, it’s no coincidence. This supplement of Ayurvedic origin has gone from the shelves of specialty health stores to the aisles of major supermarkets in less than a decade, and the interest it generates is more than just a trend. Behind the name lie decades of clinical research, placebo-controlled trials, and a plant chemistry far more complex than its image as a “stress herb” suggests. But there are also important nuances worth knowing before adding it to your routine.
When does ashwagandha start to take effect?
Expected results week by week with 300–600 mg/day of standardized extract
Begin supplementation
Take the extract with food, preferably split into two doses. The first few days may bring mild digestive discomfort that usually goes away on its own in 3–5 days. It is not a sign that something is wrong.
Nervous system adjustment
It is still too early to notice clear changes. Some people describe a slight sense of calm or slightly deeper sleep, but this is not universal. The effect on cortisol begins to activate, even if it is not yet perceptible.
First noticeable changes
This is where most people start to notice something: less reactivity to stress, an easier time falling asleep, or a mild improvement in mood. Studies confirm that cortisol reduction is already measurable in blood at this point.
Consolidation of effects
The benefits on sleep, anxiety, and physical performance consolidate. In clinical trials, the 8-week mark is the point where results are statistically robust for virtually all objectives: stress, insomnia, muscle strength, and sexual function.
Performance peak and evaluation
The 12-week mark is the most common endpoint in physical performance and VO₂ max studies. In male fertility, the most notable results — improved sperm count and testosterone — appear by 90 days. This is a good time to assess whether the supplement is delivering what you expected.
Pause or supervised continuation
Well-documented use extends up to 3 months in general, and up to 12 months in specific studies with KSM-66 without relevant laboratory abnormalities. Beyond that point, the recommendation is to take a break or continue under professional supervision, especially if you are taking other medications.
What is Ashwagandha
Ashwagandha (Withania somnifera) is an evergreen shrub of the Solanaceae family that has been part of Ayurvedic medicine in India for more than 3,000 years. Its Sanskrit name literally means “smell of horse,” referring both to the characteristic aroma of its root and to the vitality attributed to it. In the West it is popularly known as “Indian ginseng,” although it has no botanical relationship with Asian ginseng; the nickname simply reflects that both plants share a reputation as a restorative tonic.
In Ayurveda it occupies a special category: that of the Rasayana, meaning rejuvenating preparations designed to strengthen the body’s resistance against all types of stressors. And that is exactly what modern science captures under the term adaptogen, a concept that has been studied in pharmacology for decades. An adaptogen is a substance that helps the body maintain physiological balance when faced with physical or mental stress, without disrupting that balance under normal conditions. Ashwagandha consistently meets this criterion in the clinical trials published to date.
The most interesting aspect, from a functional standpoint, is understanding why it works.
Its activity is concentrated in a group of compounds called withanolides, steroidal lactones found primarily in the root. More than 75 have been identified so far, and among the most relevant are withanolide A, withanolide D, withaferine A, and withanosides. These compounds act on the hypothalamic-pituitary-adrenal axis (HPA axis), which is the circuit that regulates the production of cortisol, the hormone the body secretes in response to stress. When this axis is chronically overactivated, cortisol remains elevated and begins to affect sleep, energy, body composition, and mood. Ashwagandha works by modulating that circuit downward.
In addition to withanolides, the plant contains alkaloids such as withanine and somniferine, sitoindosides with documented anti-stress activity, saponins, and phytosterols. An action on the GABA-A receptors of the central nervous system has also been described, which partly explains its effects on anxiety and sleep. It is not a single mechanism, but a combination of pathways acting in a coordinated manner.
The part of the plant with the greatest scientific support is the root, and standardized extracts obtained from it concentrate the majority of available clinical research. The leaves also contain withanolides, but in different proportions and with a different compound profile. When reading an ashwagandha supplement label, checking whether the extract comes exclusively from the root or includes leaves will give you a clue about what type of evidence supports it.
Today ashwagandha is one of the best-selling plant-based supplements in Europe and the United States. And while that sometimes generates understandable skepticism, in this case the popularity has, at least in part, a solid foundation. What follows is precisely that: the data.
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Main Benefits of Ashwagandha
Stress and Anxiety Reduction
The most studied benefit of ashwagandha is also the most sought after: its ability to reduce stress and anxiety in a measurable way, not just subjectively.
What distinguishes this plant from other “anti-stress” supplements is that its effect on serum cortisol is backed by placebo-controlled trials and real laboratory measurements. In one of the most cited trials, adults with chronic stress who took 600 mg daily of standardized extract for 60 days recorded a cortisol reduction of nearly 28%, compared to 8% in the placebo group. At the same time, scores on validated perceived stress scales fell by around 44%. Those are not small numbers.
Is ashwagandha right for you?
Check the situations that apply to your case
From clinical practice, what I usually observe is that the improvement does not come all at once. Most people start to notice something between three and four weeks: they sleep a little better, react with less intensity to situations that previously overwhelmed them, and describe a feeling that is not euphoria but simply more calm. That is precisely what is expected from an adaptogen that acts by gradually modulating the HPA axis.
A recent meta-analysis grouping twelve controlled trials confirmed a large effect size for anxiety reduction. And in 2022, an international psychiatry working group included standardized ashwagandha as a provisional recommendation for generalized anxiety disorder, marking an important step in its clinical recognition.
Sleep Improvement
The GABAergic action of ashwagandha — its ability to activate GABA-A receptors in the central nervous system — is what best explains its effect on sleep. It does not act like a sleeping pill that anesthetizes you, but rather promotes a more natural transition into rest.
A meta-analysis published in 2021 analyzing five clinical trials with more than 400 participants found statistically significant improvements in several objective parameters: sleep latency (the time it takes to fall asleep) was reduced, sleep efficiency increased, nocturnal wakefulness decreased, and overall sleep quality improved. The effects were more pronounced in people with diagnosed insomnia, and also in those taking 600 mg per day for at least eight weeks. With lower doses or shorter periods, results are more modest.
In practice, taking it at night — one to two hours before bed — appears to yield better results when the primary goal is sleep. And unlike benzodiazepines or other hypnotics, it does not produce tolerance or dependence with continued use within the studied periods.
Physical Performance and Vitality
Here the evidence is quite concrete. In a trial involving men doing strength training, those who took 600 mg daily of KSM-66 for eight weeks gained 46 kg in their bench press one-rep max, compared to 26 kg in the placebo group. The difference in leg extension was also statistically significant. Additionally, markers of muscle damage — measured by creatine kinase in blood — were lower in the ashwagandha group, suggesting better muscle recovery after exertion.
Regarding cardiovascular endurance, several trials in athletes and healthy adults show VO₂ max increases of between 4 and 6 ml/kg/min after twelve weeks of supplementation, an improvement that is perfectly perceptible in terms of aerobic performance. A recent meta-analysis on sport and ashwagandha confirmed this effect with a mean difference of +4 ml/min/kg versus placebo.
The plant does not appear on the WADA list of prohibited substances, so it is an option that athletes can consider without concerns in that regard. Combined with its short-term safety profile, this makes it particularly interesting for active individuals looking for support during periods of intense training.
Cognitive and Sexual Health
Less well known but equally supported is the effect of ashwagandha on cognition. In trials conducted in adults with mild cognitive impairment, supplementation with 600 mg daily for eight weeks produced measurable improvements in immediate memory, executive function, sustained attention, and processing speed, assessed with standardized neuropsychological tests. The effect is not spectacular, but for people who notice that “their mind isn’t what it used to be,” it may be meaningful.
Regarding sexual and hormonal health, data are divided by sex. In men, several trials document testosterone increases of between 14% and 17%, along with improvements in semen quality — count, motility, and morphology — after periods of 8 to 12 weeks. In women, trials using 600 mg daily of root extract showed improvements in desire, arousal, lubrication, and sexual satisfaction, measured with validated scales such as the FSFI, and a reduction in distress associated with sexual dysfunction.
What underlies both cases is, once again, cortisol regulation. When chronic stress suppresses the reproductive axis, normalizing that response has cascading effects on libido and hormonal function in general.
Contraindications and Side Effects of Ashwagandha
Ashwagandha has a reasonable safety profile when used in standardized extracts and for defined periods, but that does not mean it is suitable for everyone. As with any active supplement, there are situations where the risks outweigh the potential benefits, and it is worth knowing them before starting.
Mild Effects
The most frequent side effects are gastrointestinal: nausea, diarrhea, and stomach upset, especially when taken on an empty stomach or at the start of supplementation. Drowsiness may also occur, particularly with high doses or in people especially sensitive to its action on the central nervous system. Taking it with food significantly reduces these effects, and in most cases they resolve on their own within the first few days.
Pregnancy and Breastfeeding
Use during pregnancy is clearly discouraged. Withaferine A, one of the plant’s main withanolides, has shown potential to stimulate uterine contractions in animal models, posing a real risk that should not be minimized. During breastfeeding, there is simply not enough data to guarantee safety, so the recommendation is to avoid it during that period as well.
Specific Conditions
There are three clinical situations where the contraindication is especially important. The first is hyperthyroidism: ashwagandha stimulates the production of thyroid hormones T3 and T4, which may be useful in subclinical hypothyroidism, but can worsen the condition in a patient with an already overactive thyroid. Cases of thyrotoxicosis associated with its use have been documented. The second is autoimmune diseases — lupus, multiple sclerosis, rheumatoid arthritis, Hashimoto’s — where the immune stimulation exerted by the plant may be counterproductive. The third is hormone-sensitive prostate cancer, because by raising testosterone levels it could promote tumor progression.
There is also a safety signal that deserves attention. Since 2020, documented cases of hepatotoxicity associated with ashwagandha consumption have been published, with cholestatic or mixed patterns, in patients from Iceland, the United States, Japan, Germany, and India. These cases are infrequent, but some have been severe. Therefore, if you have pre-existing liver disease or are taking medication with hepatotoxic potential, consult your doctor first, and if jaundice, dark urine, or unusual fatigue appears during supplementation, discontinue it and seek medical attention.
Interactions
The most relevant pharmacological interactions affect several drug groups. With sedatives and benzodiazepines — diazepam, alprazolam, zolpidem — the GABAergic effect of the plant can potentiate sedation in an uncontrolled manner. With levothyroxine and other thyroid medications, the risk is functional overdose if ashwagandha additionally raises T3 and T4. With antidiabetics — insulin, metformin, sulfonylureas — it can lower blood glucose more than expected. And with antihypertensives, it can add a hypotensive effect that in some patients proves excessive. If you take any of these medications, do not combine them without medical supervision.
Regarding dosage, the range most supported by clinical evidence is 300 to 600 mg daily of standardized root extract, preferably divided into two doses and taken with food. Patented extracts with the greatest scientific basis — KSM-66, Sensoril, and Shoden — vary in withanolide concentration, so the equivalent dose is not always the same across brands. Well-studied continuous use extends to three months, although some recent studies with KSM-66 have followed participants for up to twelve months without relevant laboratory abnormalities. Beyond that time, the evidence is still limited.
References
- Chandrasekhar, K., Kapoor, J. and Anishetty, S. (2012). A Prospective, Randomized Double-Blind, Placebo-Controlled Study of Safety and Efficacy of a High-Concentration Full-Spectrum Extract of Ashwagandha Root in Reducing Stress and Anxiety in Adults. Indian Journal of Psychological Medicine. https://pmc.ncbi.nlm.nih.gov/articles/PMC3573577/
- Cheah, K.L. et al. (2021). Effect of Ashwagandha (Withania somnifera) extract on sleep: A systematic review and meta-analysis. PLOS ONE. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0257843
- Wankhede, S. et al. (2015). Examining the effect of Withania somnifera supplementation on muscle strength and recovery. Journal of the International Society of Sports Nutrition. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4658772/
- Björnsson, H.K. et al. (2020). Ashwagandha-induced liver injury: A case series from Iceland and the US Drug-Induced Liver Injury Network. Liver International. https://pmc.ncbi.nlm.nih.gov/articles/PMC8041491/
- National Center for Complementary and Integrative Health – NIH. Ashwagandha: Usefulness and Safety. https://www.nccih.nih.gov/health/ashwagandha
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