Ashwagandha extract is a concentrated supplement made from the root (and sometimes leaves) of Withania somnifera, a shrub native to India and parts of Africa. It’s one of the most widely used adaptogens, a category of plants believed to help the body manage stress. The extract concentrates the plant’s active compounds, called withanolides, into capsule or powder form at levels far higher than you’d get from consuming the raw root.
What’s Actually in the Extract
The key compounds in ashwagandha are withanolides, a family of over 300 naturally occurring plant chemicals with a steroid-like structure. The ones that matter most for the effects people are after are withaferin-A, withanolide-D, and withanone. These are the compounds that clinical trials have focused on, and the ones that supplement manufacturers standardize their products around.
When you see a percentage on a supplement label, it refers to the withanolide concentration. The three most common branded extracts illustrate the range. KSM-66 is a root-only extract standardized to 5% withanolides, which reflects the natural concentration found in the root. Sensoril, made from both root and leaf, concentrates withanolides to 10%. Shoden pushes that to 35%, meaning a much smaller dose delivers a comparable amount of active compounds. This is why dosing varies so much between products: 120 mg of a 35% extract can deliver more withanolides than 600 mg of a 5% extract.
How It Works in the Body
Ashwagandha’s effects on stress and mood appear to center on the body’s cortisol system. Your hypothalamic-pituitary-adrenal (HPA) axis is the hormonal chain of command that controls your stress response, and withanolides seem to interact with it in two ways. They appear to act directly on cortisol receptors and influence the HPA axis itself. They also work indirectly by modulating GABA, the brain’s primary calming neurotransmitter, which produces sedative and relaxing effects.
The full mechanism isn’t completely mapped out. There’s evidence that withanolides may also interfere with the enzymes involved in producing stress hormones in the adrenal glands, which could partially explain why long-term, high-dose use has occasionally led to suppressed adrenal function in case reports.
Stress and Anxiety
Stress reduction is the most studied use of ashwagandha extract. Clinical trials have used doses ranging from 240 to 1,250 mg per day, though the benefits appear to be strongest at 500 to 600 mg per day. An international taskforce formed by the World Federation of Societies of Biological Psychiatry and the Canadian Network for Mood and Anxiety Treatments provisionally recommends 300 to 600 mg of root extract (standardized to 5% withanolides) for generalized anxiety disorder. That recommendation carries weight because these organizations don’t typically endorse herbal supplements.
Multiple trials show reductions in self-reported stress and anxiety scores compared to placebo, though the size of the effect varies. The type of extract and the dose of withanolides matter more than the total milligrams of powder in the capsule. If you’re comparing products, look at the withanolide content per dose rather than the total extract weight.
Sleep Quality
Ashwagandha has a measurable effect on how quickly people fall asleep. In a controlled trial comparing ashwagandha root extract to melatonin and placebo, ashwagandha reduced the time to fall asleep by about 9 minutes after four weeks and nearly 15 minutes after eight weeks, compared to roughly 4 to 7 minutes in the placebo group. Combining ashwagandha with melatonin produced the largest improvement, cutting about 21 minutes off sleep onset time by week eight.
Most sleep studies have used 250 to 600 mg per day of root extract, and the benefits appear more pronounced at 600 mg daily with at least eight weeks of consistent use. If you’re trying ashwagandha primarily for sleep, give it a full two months before deciding whether it’s working.
Physical Performance and Testosterone
A smaller but growing body of research links ashwagandha to improvements in exercise capacity. In one double-blind trial, healthy adults taking 600 mg of root extract daily for eight weeks showed statistically significant improvements in VO2 max (a measure of cardiovascular fitness) compared to placebo. Other studies have reported improvements in muscle strength and neuromuscular coordination, though these have used varying protocols.
Several trials also suggest ashwagandha may increase testosterone levels, which could partly explain the strength and recovery effects. The NIH’s Office of Dietary Supplements notes this as a consistent finding across multiple studies, though the magnitude of the increase varies.
Safety Concerns Worth Knowing
Ashwagandha is generally well tolerated in the doses used in clinical trials, but it is not risk-free. The most serious documented concern is liver injury. Case reports describe people developing significantly elevated liver enzymes after taking standard doses (around 450 mg, three times daily) for weeks to months. In one case, a 36-year-old man developed liver damage after six months of use. In another, a 30-year-old woman developed symptoms after just 45 days. Both cases involved markedly abnormal liver function tests, with ALT levels climbing to many times the normal range. These cases are rare, but they suggest that long-term daily use warrants some caution, particularly if you have any existing liver condition or take other supplements or medications that stress the liver.
Ashwagandha also affects thyroid hormone levels, which is relevant if you have a thyroid condition. Research from the Technical University of Denmark raised concerns that ashwagandha could disrupt sex hormone and thyroid function, which contributed to Denmark banning the supplement in 2023. Sweden and Finland have considered similar restrictions. In the United States, ashwagandha is sold freely as a dietary supplement without pre-market safety review by the FDA.
Pregnant women should avoid ashwagandha entirely. The same Danish research flagged potential risks of inducing miscarriage. People with autoimmune conditions are sometimes cautioned against ashwagandha because of its immune-stimulating properties, though the clinical evidence here is less definitive.
Choosing an Extract
The supplement aisle can be confusing because ashwagandha products vary enormously in what they actually deliver. Here’s what to look for:
- Withanolide percentage: This tells you the concentration of active compounds. Products range from 2.5% to 35%. A higher percentage means you need fewer milligrams.
- Plant part used: Root-only extracts (like KSM-66) are the most commonly studied. Leaf extracts contain higher concentrations of withaferin-A, which is biologically potent but also linked to more side effects at high doses.
- Standardization: Look for a product that lists the exact withanolide content per capsule, not just a vague percentage. Some labels specify this clearly (for example, “15 mg withanolides per 300 mg capsule”), which makes dosing far more predictable.
Most clinical benefits have been demonstrated with root extracts providing roughly 15 to 40 mg of withanolides per day, taken consistently for at least four to eight weeks. Starting at the lower end of the dosage range and building up is a reasonable approach, particularly since individual responses to ashwagandha vary quite a bit.