Pillar Guide  ·  Supplement Science

What Ashwagandha Actually Does (and the Side Effects to Know)

Ashwagandha (Withania somnifera) accumulated serious clinical data only in the last decade, but the record is now substantial enough to take seriously. The evidence shows reproducible cortisol reductions, meaningful sleep improvements, and modest hormonal effects. There are also real limitations, real contraindications, and an overheated corner of the supplement market that conflates preliminary findings with guaranteed outcomes. This guide covers what the research supports, what it does not, how to dose correctly, and when to skip it entirely.

01What ashwagandha actually is

Ashwagandha is the root of Withania somnifera, a small shrub native to India, North Africa, and parts of the Mediterranean. It is classified as an adaptogen: a compound that may help the body maintain equilibrium under physiological stress. The active compounds are primarily withanolides, a class of naturally occurring steroidal lactones concentrated in the root, along with alkaloids and saponins.

Not all ashwagandha extracts are equivalent. Standardized root extracts with a verified, consistent withanolide content are what most clinical trials used. The most widely studied is KSM-66, a full-spectrum root extract standardized to a minimum of 5% withanolides, produced without alcohol or chemical solvents. Most of the trials cited in this guide used KSM-66 or a comparable standardized root extract. Raw powder, leaf extracts, and unstandardized products have a different chemical profile and a much thinner evidence base.

The proposed mechanism runs primarily through the hypothalamic-pituitary-adrenal (HPA) axis: withanolides appear to modulate cortisol secretion and dampen the HPA stress response, which has downstream effects on sleep, immune function, inflammation, and sex hormones. Cortisol is the master stress hormone, and when it runs chronically elevated, it suppresses collagen synthesis in skin fibroblasts,¹ disrupts sleep architecture, blunts sex hormone production, and impairs recovery from exercise. Lowering cortisol is not a narrow benefit.

02Cortisol and stress: what the data shows

The cortisol evidence is the most robust area of ashwagandha research. Multiple independent RCTs, now synthesized in a formal meta-analysis, consistently show measurable reductions in serum cortisol.

The landmark 2012 Chandrasekhar trial enrolled 64 chronically stressed adults and randomized them to 300 mg twice daily (600 mg total) of a high-concentration root extract or placebo for 60 days. The ashwagandha group showed a 27.9% reduction in serum cortisol versus only 7.9% for placebo (P=0.0006), alongside significant improvements on all validated stress and anxiety scales.²

A separate 2019 Cureus trial tested two doses: 250 mg and 600 mg per day. Both produced statistically significant cortisol reductions (250 mg: P<0.05; 600 mg: P<0.0001) and improved sleep quality scores versus placebo.³ This dose-response relationship matters: lower doses produce a real but smaller effect; the full 600 mg dose provides the most consistent result across outcomes.

A 2023 Medicine (Baltimore) trial using 500 mg/day plus 5 mg piperine found greater morning salivary cortisol reductions alongside increased urinary serotonin and improved scores on the PSS (Perceived Stress Scale), GAD-7, and quality-of-life metrics.⁴ The piperine addition enhances absorption of withanolides, not marketing filler: it is the same black pepper extract used in pharmaceutical absorption studies.

The 2025 BJPsych Open meta-analysis of 15 RCTs (873 participants) confirmed the cortisol signal: mean reduction of 2.36 units (95% CI -3.26 to -1.46, P<0.0001) at 8 weeks.⁵ However, a separate 2025 Phytotherapy Research analysis flagged something worth understanding: ashwagandha consistently reduces measured cortisol biomarkers, but does not always reduce self-reported perceived stress to the same degree.⁶ The physiology is moving even when the subjective feeling lags. This dissociation is worth knowing so expectations are calibrated correctly.

For context on why cortisol matters beyond mood: chronic moderate psychological stress has been documented to reduce antioxidant capacity by 12%, increase visible fine lines by 33%, impair skin barrier proteins (filaggrin and loricrin), and slow fibroblast wound healing by 73% in a 2024 clinical study.⁷ Stress is not only a mental experience. Its biological footprint is measurable and visible.

03Sleep quality: the overlooked benefit

Sleep is where ashwagandha's cortisol mechanism becomes most immediately practical. Elevated evening cortisol delays sleep onset, fragments slow-wave sleep, and reduces total restorative sleep time. By modulating HPA activity, ashwagandha addresses sleep at the source rather than applying sedation.

A 2019 study specifically targeting sleep enrolled 60 adults with insomnia complaints and used 300 mg twice daily (600 mg total) of KSM-66 for 10 weeks. The ashwagandha group showed 72% improvement on the Sleep Quality Index versus 29% for placebo, with significantly better sleep onset latency, total sleep time, and morning alertness.⁸ These are meaningful clinical outcomes by any standard.

The 2019 Cureus trial (250 mg and 600 mg per day) also reported improved sleep quality as a secondary outcome at both doses, consistent with the sleep-quality signal appearing even below the 600 mg threshold.³

This matters because poor sleep is not just uncomfortable. Restricted sleep impairs skin barrier recovery, reduces skin hydration and elasticity, slows wound healing, and visibly alters facial appearance in ways that observers rate as less healthy and attractive in controlled studies.⁹ Sleep is one of the highest-leverage variables for physical appearance and recovery, and ashwagandha's sleep benefit is better supported by evidence than almost any other effect attributed to it. For how it fits a broader recovery approach, see MAXXING's supplement stacking guide.

04Workout recovery and physical performance

Ashwagandha's recovery and performance data is solid enough that it has been adopted seriously in sports supplement contexts, not just wellness. The mechanism is multi-pronged: lower cortisol supports faster muscle protein synthesis (cortisol is catabolic and suppresses protein anabolism), and direct anti-inflammatory activity from withanolides may accelerate post-exercise repair.

A 2015 Journal of the International Society of Sports Nutrition trial with 57 adults randomized to 300 mg twice daily of KSM-66 for 8 weeks showed significantly greater increases in muscle strength (bench press and leg extension), faster muscle recovery, and a higher testosterone-to-cortisol ratio versus placebo.¹⁰ Serum cortisol was significantly lower in the ashwagandha group after exercise stress, and muscle damage markers (creatine kinase) recovered faster.

The cardiorespiratory finding is less widely discussed: KSM-66 at 600 mg/day for 8 weeks produced a 13.6% improvement in VO2 max in healthy athletic adults versus placebo. VO2 max is an objective, difficult-to-manipulate measure of aerobic capacity, making this one of the more credible performance results in adaptogen research.

The practical implication for anyone in a gymmaxxing routine: ashwagandha is not a replacement for progressive overload or adequate protein intake. It fits best as a consistency tool, supporting more complete recovery between sessions, which compounds over time. See MAXXING's best looksmaxxing supplements guide for the full context of how recovery supplements fit together.

05The testosterone question

Testosterone is probably the most over-claimed benefit in ashwagandha marketing. The evidence deserves a careful read rather than a headline.

Cortisol and testosterone are physiological antagonists: elevated chronic cortisol suppresses gonadal cell function, reducing testosterone output. By reducing cortisol, ashwagandha can raise testosterone indirectly, particularly in people whose levels are suppressed by chronic stress or suboptimal lifestyle. The 2015 Wankhede trial in 57 adults undergoing resistance training reported a 15.3% increase in total testosterone versus 2.7% in placebo.¹⁰

A separate study in adults with fertility concerns (oligospermia) found KSM-66 at 675 mg/day for 90 days significantly improved sperm concentration, motility, and semen volume, alongside a 17% increase in testosterone and a 36% reduction in FSH.¹¹ The effect in a population with genuine baseline suppression is real and clinically meaningful.

The honest caveat: in adults with already-normal testosterone, the effect is smaller and less consistent. Ashwagandha is not an androgen compound. It does not directly stimulate testosterone synthesis the way luteinizing hormone would. The testosterone signal appears largely downstream of cortisol reduction. If your cortisol is well-regulated and your testosterone is already in a healthy range, the effect on that number specifically will likely be negligible.

Testosterone health is relevant across all adults, not a narrowly male concern. It plays roles in energy, mood, muscle retention, libido, and bone density regardless of gender. The data from specific male-cohort studies provides useful context without defining who the supplement is for. See MAXXING's skin and hair supplement guide for how hormone-adjacent supplements fit a broader protocol.

06Hormonal health and adrenal function broadly

Beyond testosterone, ashwagandha's effects on the HPA axis touch a wider hormonal picture. Cortisol dysregulation has downstream effects on thyroid function, DHEA-S levels, insulin sensitivity, and inflammatory cytokines. The 2019 Shoden trial (240 mg/day for 60 days) reported significant reductions in morning cortisol and DHEA-S.¹² DHEA-S is a precursor to multiple sex hormones, and its regulation reflects overall adrenal axis health rather than any single hormone in isolation.

For people managing stress from high-output work, intensive training, poor sleep, or any combination of the three, the HPA-modulating effect is relevant as an overall load-reducer. Chronic HPA activation drives low-grade systemic inflammation, impairs collagen synthesis in skin, and accelerates cellular aging via telomere attrition and mitochondrial reactive oxygen species overproduction.¹³ Modulating that axis supports more than just mood.

One note for anyone monitoring thyroid levels: ashwagandha has shown thyroid-stimulating activity in some studies, raising serum T3 and T4. For people with no thyroid issues this is not a problem and may be a modest benefit. For anyone with existing thyroid dysfunction or who takes thyroid medication, this is a meaningful contraindication to discuss with a physician before starting. More in the side effects section below.

07Ashwagandha products compared: what the specs actually say

The ashwagandha market has a quality-spectrum problem. At one end: standardized, root-only KSM-66 extracts at 5% withanolides with a clinical data trail. At the other: loosely standardized powders, leaf-and-root blends with higher withaferin A content, and undisclosed concentrations inside proprietary blends. The table below compares real products by their actual published specifications, with all brand identities anonymized. MAXXING's Chill Pill is the highlighted row.

The practical read: the market for 600 mg KSM-66 at 5% withanolides is fairly commoditized. Most products in this tier deliver the dose the clinical literature supports. Differentiators come down to absorption enhancers (piperine/BioPerine and AstraGin are both evidence-based), bottle economy (a 30-day supply at higher cost per serving vs a 60-day supply), and third-party testing transparency. MAXXING's Chill Pill includes piperine for absorption and is formulated to the clinically tested dose and extract standard.

What to avoid: undisclosed withanolide percentages, proprietary blends where the ashwagandha dose is hidden, leaf-and-root combination products (leaf extract carries higher withaferin A, which at elevated concentrations has shown cytotoxic effects in cell studies), and unstandardized raw powder capsules marketed as premium. The cheapest option is only good value if you know what is actually in it.

08Side effects to actually know

Most ashwagandha marketing buries or ignores side effects. The following is a sourced account of what is documented, organized by clinical significance.

Gastrointestinal discomfort

The most commonly reported side effects are GI: nausea, loose stools, stomach upset, and cramping. These are more frequent at doses above 600 mg/day and when taken on an empty stomach. Most RCTs at the standard 600 mg daily dose report low rates of GI adverse events, and they largely resolve by taking the supplement with food. This is the side effect most people encounter and the easiest to manage.

Drowsiness

Ashwagandha's cortisol-lowering and sleep-supporting effect can translate to daytime drowsiness, particularly in people sensitive to its calming action or those who take it in the morning. This is not universal, but it is common enough that evening dosing is a sensible default if your schedule allows it.

Thyroid hormone effects

This is the most clinically important side effect for a specific subgroup. Ashwagandha has been shown to stimulate thyroid activity, increasing serum T3 and T4 levels in some studies. For healthy people with normal thyroid function, this is not a concern. For people with hyperthyroidism, Graves' disease, or who take thyroid hormone medication, this effect can be destabilizing. If you have any thyroid diagnosis, discuss ashwagandha with your physician before starting.

Liver-related case reports

There are isolated case reports of hepatotoxicity attributed to ashwagandha. The mechanism is not confirmed, and most reports involved high doses or multi-supplement combinations, making causality difficult to establish. The absolute risk appears low given global consumption volumes versus the number of reports, but it is worth knowing. Anyone who develops jaundice, abdominal pain, or dark urine while taking ashwagandha should stop immediately and see a doctor.

Drug interactions

Documented interaction categories include: sedatives and benzodiazepines (additive CNS depression); thyroid medications (additive effect on thyroid hormones); immunosuppressants (ashwagandha has immunomodulating effects that could theoretically work against suppression therapy); and medications metabolized by the liver CYP450 system. If you take any prescription medication, a pharmacist interaction check is a simple and sensible step before starting.

Contraindication in pregnancy

Ashwagandha has traditional use as a uterine stimulant in Ayurvedic practice. It is contraindicated during pregnancy and for people who are breastfeeding. Do not use it during pregnancy.

09Dosing, timing, and what KSM-66 means

The clinical evidence clusters around two effective dose ranges:

• 240 to 300 mg/day: Measurable cortisol and stress-score reductions documented in the Shoden trial (240 mg) and the lower arm of the 2019 Cureus trial (250 mg). This is a real dose with clinical support, not a placebo-equivalent. Suitable for those starting conservatively or sensitive to supplements.
• 600 mg/day: The most consistently effective dose across the majority of RCTs, including the largest meta-analysis. Most trials split this as 300 mg twice daily with food. This is the dose used in the cortisol, sleep, and recovery trials producing the strongest effects.

Going above 600 mg per day (some products push 1,000 mg) does not have proportionally stronger clinical support and increases GI side effect risk. The dose-response curve appears to plateau around the 600 mg mark for most outcomes.

On timing: most RCTs dosed in the morning, once or twice daily with food. For sleep quality as a primary goal, evening dosing makes practical sense. For performance and recovery, morning dosing or split dosing aligns with the trial protocols. Consistency across days matters far more than the specific clock time.

On the time horizon: expect 4 weeks minimum before drawing any conclusions, and 8 weeks to see the full effect profile the trials document. Ashwagandha is not acutely stimulating. If you take it once and feel nothing, that is expected and not informative. The effect builds with sustained daily use.

What KSM-66 actually means: it is a proprietary branded extract with specific processing (water and milk extraction, no alcohol solvents) and root-only sourcing. This produces a specific withanolide profile with low withaferin A content. Withaferin A at high concentrations has shown cytotoxic effects in cell models, so the low content in root-only extracts is a relevant safety consideration. Not every product labeled "ashwagandha root extract" is equivalent to KSM-66. The 5% withanolide standardization is the key specification to verify.

MAXXING's Chill Pill uses KSM-66 at 600 mg with piperine for absorption, formulated to match the dose profile with the strongest evidence base. For how it integrates with a broader supplement protocol, see the supplement stacking guide.

10Who should avoid ashwagandha

The following groups should not use ashwagandha without explicit medical clearance:

• Pregnant or breastfeeding: Contraindicated. The uterine-stimulant properties are documented in traditional and modern literature. No exceptions.
• Thyroid disorders (hyper- or hypothyroidism): Ashwagandha can alter thyroid hormone levels (T3/T4). Anyone on levothyroxine, methimazole, or other thyroid medications should consult their prescriber before use.
• Autoimmune conditions: Ashwagandha has immunomodulating effects. For people with lupus, rheumatoid arthritis, multiple sclerosis, or who take immunosuppressants, this interaction could be problematic. Medical guidance is needed.
• Sedative medications: Additive CNS depression is possible with benzodiazepines, barbiturates, and sleep medications.
• Liver conditions or elevated liver enzymes: Given the rare hepatotoxicity case reports, anyone with existing liver issues or abnormal liver function tests should avoid it without medical clearance.
• Surgery scheduled within 2 weeks: Ashwagandha may amplify anesthesia effects and affect blood pressure. Standard pre-surgical supplement-pause protocols apply.

If none of the above apply and you are a healthy adult, the safety profile at 600 mg/day of a standardized extract is well-documented across multiple 60-day trials with no significant adverse events reported in the active groups. The concern is not for the general population; it is for the specific subgroups listed above.

11FAQ