Ashwagandha generally does not keep you awake. In clinical trials, it consistently improves sleep quality, helps people fall asleep faster, and increases total sleep time. Its name literally translates from Sanskrit as “smell of the horse,” but its species name, somnifera, means “sleep-inducing.” That said, a small number of people do report feeling more alert or energized after taking it, and certain circumstances can tip ashwagandha from calming to stimulating.
What the Sleep Research Shows
Across multiple human trials, ashwagandha has been tested at doses ranging from 120 to 1,250 mg per day for 4 to 12 weeks. The most common dose studied is 600 mg daily. In these trials, participants showed significant improvements in sleep efficiency, total sleep time, and sleep latency (the time it takes to fall asleep), along with fewer awakenings during the night.
In one trial of 150 adults with self-reported sleep problems, 72% of those taking ashwagandha reported improved sleep quality after six weeks, compared to 29% in the placebo group. Wrist-worn activity monitors confirmed the subjective reports: participants genuinely spent more of their time in bed actually sleeping. A separate trial in 80 adults found that those with insomnia who took ashwagandha showed improvements in sleep quality, how quickly they fell asleep, and how alert they felt in the morning. A 2021 meta-analysis pooling five of these trials reached the same conclusion.
How It Promotes Sleep
Ashwagandha works on sleep primarily through two pathways. First, it lowers cortisol, the body’s main stress hormone. In stressed adults, ashwagandha reduced morning cortisol levels by about 23% over the course of a study. High cortisol at night is one of the most common reasons people lie awake with a racing mind, so bringing it down can make a real difference in how easily you wind down.
Second, ashwagandha’s active compounds (called withanolides) appear to enhance the activity of GABA, a brain chemical that quiets neural activity. This is the same system targeted by many prescription sleep and anti-anxiety medications, though ashwagandha’s effect is much milder. Animal research has shown that ashwagandha increased deep, slow-wave sleep and even counteracted caffeine-induced insomnia in a dose-dependent way, meaning higher doses produced a stronger sleep-promoting effect.
Why It Keeps Some People Awake
Despite the overall trend toward better sleep, some people experience the opposite. There are a few reasons this happens.
Thyroid stimulation. Ashwagandha can increase thyroid hormone activity. Animal studies have shown it boosting the main thyroid hormone (T4) by as much as 111%. For someone whose thyroid function is already normal or on the high end, this push can tip them toward symptoms of an overactive thyroid: increased heart rate, anxiety, restlessness, and difficulty sleeping. Case reports have documented thyrotoxicosis (excess thyroid hormone) in people taking ashwagandha supplements, with symptoms including palpitations, tremor, and irritability. Some commercial ashwagandha products have even been found to contain thyroid hormones at levels that could cause problems on their own.
Daytime energy boost. Ashwagandha doesn’t just sedate. In older adults, it improved mental alertness and reduced daytime sleepiness. For some people, particularly those who aren’t sleep-deprived or highly stressed, the dominant effect is increased energy and focus rather than relaxation. This is more likely to cause wakefulness if you take it close to bedtime.
Vivid dreams and disrupted sleep. Clinical trials have reported drowsiness in up to 21% of participants taking ashwagandha. But the supplement has also been linked to unusually vivid or strange dreams, especially during the first few days. For some users, these dreams are disruptive enough to fragment sleep and leave them feeling like they didn’t rest well, even if they technically slept through the night. These effects often diminish with continued use.
Timing and Dosage Matter
When you take ashwagandha can shift whether it feels calming or energizing. If your goal is sleep, taking it in the evening gives its cortisol-lowering and GABA-enhancing effects the best chance to work when you need them. If you find it gives you energy or mental clarity, morning dosing keeps that effect useful rather than disruptive.
The clinical trials that showed sleep benefits used doses between 120 mg and 600 mg daily, depending on the extract. Lower-dose, highly concentrated extracts (like Shoden at 120 mg per day) produced comparable results to higher-dose root extracts (like KSM-66 at 600 mg per day) because they contain different concentrations of active compounds. Starting at the lower end of the dosage range and adjusting based on your response is a practical approach. Individual responses vary enough that experimentation with timing and dose is genuinely necessary rather than optional.
Who Should Be Cautious
If you have a thyroid condition, especially hyperthyroidism or Graves’ disease, ashwagandha’s thyroid-stimulating effects make it a poor fit. People already taking thyroid medication should be particularly careful, since ashwagandha could amplify the medication’s effects unpredictably.
If you’re a naturally light sleeper or someone sensitive to supplements that affect brain chemistry, the vivid dream effect or the initial adjustment period could temporarily worsen your sleep before it improves. Most studies show benefits emerging over several weeks, not overnight, so a rough first few nights doesn’t necessarily predict the long-term effect.
People taking sedative medications or other supplements that enhance GABA activity should be aware that ashwagandha works on the same system. Combining them could lead to excessive drowsiness, confusion, or next-day grogginess rather than the balanced improvement seen in clinical trials.