Ashwagandha Benefits and Side Effects: The Balanced Guide

This is ashwagandha's most replicated and consistent clinical benefit. A randomised double-blind placebo-controlled trial published in Medicine gave 60 stressed adults either 240mg of a standardised ashwagandha extract (Shoden) or placebo daily for 60 days. The ashwagandha group showed statistically significant reductions on the Hamilton Anxiety Rating Scale (HAM-A) and significantly lower morning cortisol levels compared to placebo. The proposed mechanism is modulation of the hypothalamus-pituitary-adrenal (HPA) axis - the system that governs the body's stress response.

Multiple other trials using different standardised extracts (KSM-66, Sensoril) have produced similar findings: reduced perceived stress scores, lower self-reported anxiety, and measurable cortisol reductions. The consistency across different extracts and research groups gives this benefit more credibility than most. The key qualifier is that these trials used standardised, withanolide-rich extracts, not uncharacterised root powder. For more on the magnesium and nervous system connection that complements ashwagandha, see the article on magnesium for anxiety.

A systematic review and meta-analysis of five randomised controlled trials published in PLoS ONE found that ashwagandha extract produced a small but statistically significant improvement in overall sleep quality (SMD -0.59; 95% CI -0.75 to -0.42). The effect was more pronounced in people with diagnosed insomnia, at doses of 600mg per day or above, and with treatment durations of at least eight weeks. Secondary outcomes included improved mental alertness on rising and reduced anxiety.

The mechanism likely overlaps with its cortisol-lowering effect, since high evening cortisol is one of the main physiological barriers to falling asleep. Ashwagandha is a useful addition to a sleep protocol but not a replacement for foundational sleep habits. For the full picture, see the guides on common causes of insomnia, evidence-based sleep supplements, and evening habits that improve sleep.

Several trials report reductions in fatigue scores and improvements in perceived energy, particularly in people whose fatigue is driven by chronic stress or suboptimal sleep. Ashwagandha's adaptogenic properties - its ability to help the body manage physiological stress load - are the plausible mechanism. If your fatigue is rooted in poor sleep and high cortisol, ashwagandha may help address both drivers simultaneously.

The evidence for direct stimulant-like energy is weaker. Ashwagandha does not raise alertness the way caffeine does, and it should not be expected to. Where it performs better is in reducing the drag that stress and poor sleep create over time rather than producing an acute energy lift. For a broader range of evidence-based approaches, see the article on how to boost energy naturally.

A systematic review and Bayesian meta-analysis of 13 clinical trials found that ashwagandha supplementation outperformed placebo on strength and power, cardiorespiratory fitness, and fatigue and recovery variables in healthy adults. The effect sizes were in the low-to-moderate range. The proposed mechanisms include reduced exercise-induced cortisol, lower muscle damage markers, and improved VO2 max.

These are relevant outcomes for recreational athletes and people managing training load, though they are based on relatively small trials. The authors noted that more comparable studies are needed to firm up the effect estimates. For the magnesium side of exercise recovery, see magnesium for exercise.

Ashwagandha is sometimes marketed for blood sugar control, testosterone support, thyroid function, and cognitive performance. The evidence in each of these areas exists but is substantially thinner than for stress and sleep, and the commercial claims often outrun what the research actually demonstrates.

Blood glucose and insulin sensitivity improvements have been seen in some diabetic and pre-diabetic populations, likely through mechanisms involving cortisol reduction. These findings are interesting but are based on a small number of trials. Testosterone increases have been reported primarily in men with low baseline levels or under significant physical stress - trials in healthy men with normal testosterone tend to show smaller or inconsistent effects. Women seeking hormonal benefits should be particularly cautious about extrapolating from male-only data.

The biggest source of inconsistency across ashwagandha research is extract standardisation. Different products contain wildly different concentrations of withanolides, the active compounds responsible for ashwagandha's pharmacological effects. A root powder with no standardisation guarantee may contain anywhere from negligible to moderate withanolide content depending on growing conditions and processing.

Trials that use verified, standardised extracts (KSM-66 typically standardised to 5% withanolides, Sensoril to 10% withanamide-type withanolides) consistently produce stronger and more reliable results than trials using generic ashwagandha powder. Other sources of inconsistency include variation in dose (trials range from 120mg to 1,500mg per day), duration (four weeks to six months), and the populations studied. Results in high-stress, sleep-deprived, or physically active populations tend to be stronger than in healthy, low-stress populations where there is less room for improvement.

What "short-term use" means in the research

The vast majority of clinical trials run for eight to twelve weeks. Long-term safety data beyond that window is limited. We know ashwagandha appears safe and effective at standard doses over two to three months, and it has a long history of traditional use, but the formal evidence base does not yet provide confident safety data beyond that window.

Most practitioners who recommend ashwagandha suggest cycling it: eight to twelve weeks on, a break of four weeks, then reassessing. There is no strong clinical data to prescribe an exact cycling protocol, but the principle of not treating a supplement with limited long-term data as indefinitely safe is sound.

In clinical trials at standard doses, ashwagandha is generally well tolerated. The most commonly reported side effects are mild gastrointestinal symptoms: loose stools, nausea, or mild stomach discomfort, usually at higher doses or on an empty stomach. These typically resolve with dose adjustment or taking the supplement with food.

Liver toxicity - rare but real

A case series published in Liver International described five patients who developed drug-induced liver injury (DILI) attributed to ashwagandha-containing supplements, identified across Iceland and the US Drug-Induced Liver Injury Network. All five developed jaundice and symptoms including nausea, lethargy, and abdominal discomfort within 2 to 12 weeks of starting the supplement. The pattern of injury was cholestatic or mixed. No patient developed liver failure, and liver tests normalised within one to five months after stopping. Chemical analysis confirmed ashwagandha in all available supplements.

A 2023 review of ashwagandha hepatotoxicity cases published in Pharmaceuticals confirmed multiple documented cases of herb-induced liver injury, noting that both inherent herb properties and contamination or adulteration of supplement products may contribute to hepatotoxicity risk. This underscores the importance of product quality and third-party testing. One reviewed case progressed to liver transplantation.

These cases are uncommon relative to the very large number of people using ashwagandha globally, but they are not theoretical. Any supplement that can cause liver injury in rare cases warrants transparent communication of that risk.

Pregnancy and breastfeeding

Ashwagandha is contraindicated during pregnancy. Animal studies suggest it may have abortifacient properties at high doses, and there is no adequate human safety data for use during pregnancy or breastfeeding. Avoid it in both contexts until the evidence base changes.

Thyroid conditions

Ashwagandha appears to stimulate thyroid hormone production. A randomised controlled trial in subclinical hypothyroid patients found that ashwagandha significantly increased T3 and T4 levels and decreased TSH, consistent with stimulation of thyroid activity. This may be beneficial in people with subclinical hypothyroidism, but it creates a genuine risk for people with hyperthyroidism or Graves' disease. If you have any thyroid condition or are on thyroid medication, check with your GP before using ashwagandha.

Liver disease history

Given the documented hepatotoxicity cases, people with existing liver disease, elevated liver enzymes, or a history of drug-induced liver injury should avoid ashwagandha or use it only under medical supervision with periodic liver function monitoring. The liver injury cases reported were in people with no prior liver conditions - existing liver vulnerability further raises that risk.

Autoimmune disease or immune-suppressing medications

Ashwagandha has immunomodulatory properties that may stimulate immune activity. In people with autoimmune conditions (lupus, rheumatoid arthritis, multiple sclerosis) or those taking immunosuppressant medications, this could worsen the underlying condition or interfere with drug action. Seek specific medical advice before use.

Children and adolescents

Clinical trials have been conducted exclusively in adults. There is no adequate safety or dosing data for children or adolescents. Use in this group is not supported by the evidence and should be avoided.

Product quality matters more with ashwagandha than with many other supplements, for two reasons: standardisation directly affects efficacy, and contamination or adulteration is a documented concern that can contribute to the liver toxicity cases described above.

Biosphere Sleep contains ashwagandha alongside magnesium and other sleep-supporting ingredients. For any ashwagandha-containing product, standardised extract with verified withanolide content and third-party testing are non-negotiable.