Ashwagandha is an evergreen shrub native to parts of Africa, India, and the Middle East that has been used for centuries in traditional medicine. Today it’s one of the most popular herbal supplements in the world, primarily taken to lower stress, improve sleep, and support physical performance. The plant belongs to the same botanical family as tomatoes and peppers, and its active compounds, called withanolides, are responsible for most of its effects on the body.
How Ashwagandha Works in the Body
The primary way ashwagandha produces its calming effects is by dialing down the body’s main stress signaling system: the connection between your brain and adrenal glands known as the HPA axis. When you’re under chronic stress, this system stays activated, keeping cortisol (your main stress hormone) elevated. Ashwagandha appears to dampen that overactivity. In one clinical trial, participants taking ashwagandha saw a 23% decrease in fasting morning cortisol levels over the study period, compared to just 0.5% in the placebo group.
The plant’s steroid-like compounds may mimic certain adrenal hormones just enough to signal the brain to reduce its own stress hormone production. Ashwagandha also interacts with GABA receptors, the same calming receptors targeted by anti-anxiety medications, which helps explain the relaxation effect many users report.
Stress and Anxiety Reduction
This is where the strongest evidence sits. A systematic review and meta-analysis found that ashwagandha supplementation produced a statistically significant reduction in scores on the Perceived Stress Scale, a standard measure of how overwhelmed people feel in daily life. Cortisol levels also dropped significantly after eight weeks of supplementation. The effective dose range in most studies was 250 to 600 mg per day of a standardized extract, taken consistently for 4 to 13 weeks before results became clear.
If you’re expecting overnight relief, that timeline matters. Most people in clinical trials didn’t see meaningful changes in the first week or two. The stress-lowering effects build gradually, with the strongest results typically appearing around the eight-week mark.
Physical Performance and Fitness
Ashwagandha has gained traction in the fitness world for its effects on endurance and recovery. A meta-analysis of studies in healthy adults and athletes found a significant improvement in VO2 max, a measure of how efficiently your body uses oxygen during exercise. The average improvement was about 3 mL/kg/min, which is modest but meaningful for someone training regularly. Studies used doses ranging from 300 to 1,000 mg per day over 2 to 12 weeks, and the biggest gains came from higher total intake over the full program.
The mechanism likely involves increased hemoglobin and red blood cell production, which improves oxygen delivery to working muscles. Some research also points to benefits for muscle strength and recovery, though the evidence there is less consistent than for endurance.
Sleep Quality
Several clinical trials have tested ashwagandha for sleep, using root-only extracts and root-and-leaf combinations. Most found improvements in how quickly people fell asleep and how restful their sleep felt, particularly in people who were already dealing with stress or mild insomnia. The GABA receptor activity likely plays a role here, promoting the same kind of nervous system relaxation that helps you transition into sleep.
Common Extract Types
Not all ashwagandha supplements are the same. The three branded extracts you’ll see most often differ in which parts of the plant they use and how concentrated they are:
- KSM-66 uses only the root and is standardized to more than 5% withanolides. A typical dose is two 300 mg capsules per day. This is the most widely studied extract.
- Sensoril uses both root and leaf, which changes the balance of active compounds. It tends to have higher overall withanolide content per milligram, so doses are usually lower.
- Shoden also uses root and leaf, standardized to contain 21 mg of withanolide glycosides per 60 mg capsule. It’s the most concentrated option, requiring the smallest capsule size.
Leaves actually contain a higher percentage of withanolides (0.24%) than roots (0.04 to 0.07%), which is why leaf-inclusive extracts can pack more active compounds into a smaller dose. Root extracts, however, have a longer history of traditional use and a larger body of clinical research behind them.
Safety and Side Effects
For most people, ashwagandha at standard doses is well tolerated. But it’s not without risks. Cases of liver injury have been reported in multiple countries, including the United States, Japan, Iceland, India, and Poland. In one case, a patient developed jaundice after increasing his ashwagandha dose to two or three times the recommended amount. In another, a 39-year-old woman was hospitalized with acute liver inflammation after using a product containing ashwagandha root extract. A study of five patients who developed liver damage found that all recovered, though it took about eight months for liver function to return to normal.
These cases are rare relative to the millions of people taking ashwagandha, but they’re worth knowing about, especially if you’re taking other supplements or medications that stress the liver.
Who Should Avoid It
The National Institutes of Health specifically flags ashwagandha as not recommended for people with autoimmune disorders, thyroid conditions, or those about to have surgery. Because it can stimulate immune activity, it may worsen conditions like lupus, rheumatoid arthritis, or multiple sclerosis. It can also interact with thyroid hormone medications, potentially pushing thyroid levels out of range.
Other known interactions include medications for diabetes and high blood pressure (ashwagandha can lower both blood sugar and blood pressure on its own), immunosuppressants, sedatives, and anti-seizure drugs. Pregnant women are also advised to avoid it, as some of its compounds have shown effects on hormone levels including luteinizing hormone and follicle-stimulating hormone.