Ashwagandha: What It Actually Does, the Dose, and Whether It's Worth It

Ashwagandha (Withania somnifera) is the best-selling adaptogen on the market and one of the few herbal supplements with a decent stack of controlled trials behind it. That doesn't mean it does everything the label claims. Here's what the numbers actually show, what dose was used in research, and who can safely ignore the whole thing.

What it is and what was actually measured

It's an extract of the root (occasionally the leaf) of a nightshade-family plant. The tracked active compounds are withanolides, and nearly every serious trial used an extract standardized to 2.5–5% withanolides. Most studies ran 8 weeks, enrolled 40–120 people, and measured three things: cortisol levels, stress and sleep scales, and strength in people who had just started training.

One detail matters a lot: most participants were chronically stressed adults or people with insomnia, not well-rested athletes. The closer you are to that profile, the more likely you are to feel something.

Stress, cortisol and sleep

This is the strongest part of the evidence. In trials using 300–600 mg per day for 8 weeks, morning serum cortisol dropped roughly 20–30% from baseline, while the placebo group moved by a few percent. On perceived stress scales (PSS-10), scores fell around 30% versus about 10% for placebo.

Sleep effects are smaller but consistent: time to fall asleep shortened by roughly 10–25 minutes and sleep efficiency up 3–6%. The best results came from people with diagnosed insomnia, at doses of at least 600 mg, over at least 8 weeks.

In plain terms: ashwagandha won't knock you out like a sleeping pill and it won't fix the fact that you get into bed at 1 a.m. It slightly lowers your baseline tension, which makes falling asleep easier.

Strength, muscle and testosterone

The most-cited trial here followed 57 untrained men through 8 weeks of resistance training with 600 mg per day. The supplement group added about 46 kg to their bench press 1RM versus 26 kg for placebo, and 14.5 kg on leg extension versus 9.8 kg. Those numbers look spectacular mostly because the participants started from zero — untrained lifters improve fast at everything.

Testosterone in these studies rises about 10–15%, and mainly in stressed men or those with fertility issues, meaning people who started low. That is nowhere near the effect of any anabolic agent and shouldn't be framed that way. If you've been training 2–3 years, sleeping 7 hours and eating enough protein, the realistic contribution to your strength is small.

The dose: numbers that were actually used

• Standardized root extract: 300 mg twice per day, so 600 mg total. At 5% withanolides that's roughly 30 mg of withanolides daily.
• Plain ground root powder: 3–6 g per day, because it's far weaker than an extract.
• Timing: with food, since an empty stomach triggers nausea more often. For sleep, take the full dose 45–60 minutes before bed; for stress, split it morning and evening.
• How long: budget 4 weeks for sleep, 8 weeks for stress and training effects. Nothing here is acute, so judging it after three days is pointless.

Most trials ran up to 12 weeks, and data past 6 months is thin. A reasonable approach is 10–12 weeks on, then a 4-week break to see whether you actually miss anything.

Side effects and who should skip it

Around 5–10% of users get nausea, loose stools or daytime drowsiness. There's also a rarer but more serious issue: several dozen published cases of liver injury linked to ashwagandha, typically after 2–12 weeks of use.

Skip it if you're pregnant or breastfeeding, if you have hyperthyroidism or take thyroid medication (ashwagandha can raise T4 and lower TSH), if you take sedatives, and if you have an autoimmune condition. Stop it 2 weeks before any planned surgery because of the sedative effect.

When to see a doctor

• Stop immediately and get checked if you notice yellowing of the eyes or skin, dark urine, pale stools, pain under the right ribs, or nausea lasting more than 3–4 days.
• If you take levothyroxine, antidepressants, sedatives, immunosuppressants, or blood pressure and diabetes medication — ask before you start, not after.
• If anxiety or insomnia has been blocking your work and training for more than a month, that's a case for an appointment, not a supplement.
• If persistent fatigue comes with unexplained weight loss, you need bloodwork and a thyroid panel, not a herbal powder.

How to test it on yourself

If you want to know whether it works for you, run it honestly: 8 weeks, 600 mg per day, and no other new variable in that window. Track four numbers: minutes to fall asleep, night wakeups, a morning freshness rating from 1 to 10, and one hard training metric (reps at a fixed weight on squat or bench). Compare week 0 to week 8. If there's no difference, stop and keep your money.

The short version

• The evidence-backed dose is 300 mg twice daily of a standardized root extract, for 8–12 weeks.
• The strongest effects are on stress and sleep: cortisol down 20–30%, falling asleep 10–25 minutes faster.
• Strength and testosterone effects are real but were measured mostly in untrained and stressed people.
• Avoid it in pregnancy, on thyroid medication, alongside sedatives, or with autoimmune disease.
• Sleeping 7–9 hours, eating 1.6–2.2 g of protein per kg and training 3–4 times a week will outperform any capsule several times over.