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What Does Ashwagandha Do? I Review The Research And Discuss Its Main Health Benefits.

Ashwagandha is the common name of the Withania somnifera plant which is commonly farmed in India and has been used in traditional ayurvedic medicine for thousands of years.

Although ashwagandha is mainly used as an anxiolytic (anti-anxiety) supplement, recent studies have also suggested that ashwagandha might have other benefits– namely weight loss, an increase in testosterone and thyroid function, and even the enhancement of male fertility.

Of course, like any herbal supplement, it’s been overhyped in some corners.  Here’s I’ll explain the real deal about ashwagandha and separate fact from fiction.  

Make sure to read our article on the best ashwagandha brands!

Ashwagandha Studies

Ashwagandha For Anxiety

Anxiety reduction is the single most-studied use of ashwagandha, and this is where ashwagandha extract excels.

One study found that people with chronic stress who used 600 mg a day of full-spectrum ashwagandha had improvements in all measured stress and anxiety parameters.

Read more here.

In another study, a group of individuals used 300 mg of ashwagandha twice a day and experienced reductions in anxiety symptoms by 56%, compared to 30% for the placebo group.  The ashwagandha used in this study had 1.5% withanolide content, so this 600 mg a day equates to 9 mg of withanolides.  

In summary, studies consistently show a moderately-strong anxiolytic effect from ashwagandha, and that effect is stronger in people suffering from chronically elevated stress.  Other benefits of ashwagandha may be secondary to this anxiolytic effect, i.e. they may occur because ashwagandha reduces stress.  

Ashwagandha For Stress

Stress and anxiety are used almost interchangeably by most people, but scientists distinguish between psychological anxiety and physiological stress, which they measure primarily by blood cortisol levels.  

One study found that 600 mg a day of full-spectrum ashwagandha extract in persons with chronic stress improved all measured stress and anxiety parameters.  Most notably, it reduced cortisol levels by 26%.  

That’s huge and suggests that cortisol reduction may be one of ashwagandha’s primary, or most potent, effects.  

Ashwagandha For Sleep

If ashwagandha reduces stress and exerts an overall relaxing effect, it stands to reason that it would also be an effective sleep aid.  And in fact, it is.

A 2021 study found that ashwagandha improves sleep in adults both with and without insomnia.  In both groups, improvements were seen in both sleep latency (getting to sleep faster) and sleep efficiency (how restful sleep was).  Both groups also benefitted from improved alertness during the day.

A meta-analysis confirmed that ashwagandha improves sleep latency and quality, as well as anxiety and daytime alertness.  The effects were more prominent in people with insomnia, when dosages were at least 600 mg a day, and when the study duration was at least 8 weeks.  

Notably, ashwagandha seems to improve sleep even in people without either insomnia or chronic stress, although it is more effective in people with at least one of those conditions. 

Ashwagandha For Thyroid 

One study found that ashwagandha improves thyroid function in patients with subclinical hypothyroidism.

A team of Indian researchers found that 600 mg of ashwagandha a day increased levels of both T3 and T4 thyroid hormones.  Patients had mildly low thyroid hormone levels to begin with but were not otherwise being treated.  

This result is hard to interpret.  It could be caused by improved sleep or lower cortisol levels on ashwagandha, as cortisol can mildly impair thyroid function.  On the other hand, it could be that ashwagandha directly improves thyroid function, or perhaps raises appetite.  

In any case, this finding has not been widely replicated and more studies are needed before ashwagandha can be recommended as a thyroid support supplement with any degree of confidence.  

Ashwagandha For Testosterone And Sperm Quality

There is currently limited evidence to suggest that ashwagandha may modestly increase testosterone levels in men.

In infertile men, ashwagandha supplementation improved testosterone levels along with several fertility parameters: sperm count, motility, sperm concentration, and overall seminal volume.

Read more here.

Notably, oxidative stress was also reduced and antioxidant levels were increased.  It is suggested by the researchers that ashwagandha’s fertility benefits may have stemmed from this reduction in physiological stress parameters.

In another study of strength-training males, ashwagandha supplementation increased testosterone levels and muscle mass, as well as strength, compared to a control group.

In this case, it is likely that ashwagandha aided recovery from exercise due to a combination of improving sleep and reducing stress.  Additionally, because cortisol and testosterone are made from the same precursor hormone– pregnenolone– reducing cortisol may have allowed the body to produce more testosterone.

So far, the research strongly suggests that ashwagandha increases testosterone levels in men.  However, the effect size is fairly modest and has only been confirmed in men who are infertile or actively strength training.

Ashwagandha For Weight Loss

Ashwagandha could theoretically aid weight loss in a few different ways.  

First, increased thyroid function should speed up your metabolism.

Second, reduced anxiety and improved sleep could potentially aid with dietary self-control and emotional eating.

Finally, improved sleep, reduced cortisol, and higher testosterone could all improve nutrient partitioning, helping the body burn fat and build more muscle.

Studies have been mixed on whether this actually occurs though.  One study did indeed find weight loss from ashwagandha in patients suffering from chronic stress.  Weight loss has also been incidentally noted in other studies which were mainly focused on anxiety.

However, other studies which weighed patients found no weight loss from ashwagandha, although one found a trend towards reduced body fat despite no weight loss.  In strength-training individuals, ashwagandha improved body composition but did not reduce weight.

More studies are obviously needed, and in particular studies which specifically test for fat loss.  So far, it seems likely that ashwagandha can aid weight loss in individuals who suffer from poor sleep, chronic stress, and who find exercise and dietary adherence difficult as a result.  It may not be the best solution– there are many good fat loss supplements out there– but it’s probably somewhat effective.  

Ashwagandha Side Effects

Ashwagandha has a very mild side effect profile, at least at the dosage range of 600-900 mg per day at 1.5% withanolide concentration which is used in most studies.

Taking more than 300 mg of ashwagandha at once can cause drowsiness, and dosages this high should only be taken before bed as a sleep aid.

Long-term, it’s possible that you can build up a tolerance for ashwagandha, but so far this hasn’t been seen.  In fact, the effects seem to heighten over at least the first two months.  Longer-term studies would be helpful, but so far ashwagandha seems to be most side-effect-free.

You should, however, ask your doctor before combining ashwagandha with prescription medications, particularly sleep aids, anti-anxiety, anti-depressant, or cortisol-reducing drugs.   

Ashwagandha Dosage

The dosage used in studies is typically 600 mg a day, but 900 mg is sometimes used.  The withanolide concentration is usually between 1.5% and 5%, for a total daily withanolide intake of 9-45 mg.  Make sure to look at the withanolide content and not just the total milligrams.  

This is typically divided into dosages of 300 mg taken 2-3 times a day.  600 mg doses are sometimes taken in the evening as a sleep aid, however.  

Ashwagandha’s duration of action is unknown, as different withanolides have different half-lives, but anecdotally people find that dividing the dose works better for anxiety, and a 600 mg dose can cause drowsiness.  Therefore, it’s best to follow this divided dosage protocol.

What To Look For When Buying Ashwagandha

You should look for the following from ashwagandha products and brands:

  • First and foremost, the product needs to clearly state its withanolide content.  Never buy a supplement that doesn’t tell you how much of the active ingredient is in it!
  • The company should provide certificates of analysis from an independent lab, either (ideally) published on their website or available on request.  
  • Look for positive reviews that sound real, meaning they provide an actual description and not just hyperbolic “Wow I love this it’s so great!” language.  On Amazon, you can check the reviewer’s profiles and see what other things they’ve reviewed– look for reviewers who don’t only write five-star reviews.
  • The company should be reputable and well-established.  It should be clear about where it’s located and who runs it.
  • Look for KSM-66 ashwagandha, which is a highly-concentrated root-only extract.  It has a standardized withanolide content of 5%, making it both pure and potent.

Most of all, watch out for some of the warning signs that an online supplement company is less than legitimate.

What Are The Most Trustworthy Ashwagandha Brands?

Goli Ashwagandha Gummies

Ashwagandha extract is usually sold in capsules, and occasionally as a bulk powder.  Goli, however, takes a unique approach and offers ashwagandha gummies.

Each gummy contains 150 mg of KSM-66 ashwagandha, for 7.5 mg of withanolides.  The recommended dosage is two gummies, twice a day, but you may even want to start at half of that.  

These gummies have the advantage of being the easiest form of ashwagandha to carry around with you since, unlike capsules, you don’t need a beverage to wash them down.

Nootropics Depot

Nootropics Depot’s ashwagandha capsules contain 300 mg of KSM-66 ashwagandha extract, for 15 mg of withanolides per day.  This is one of the best-value ashwagandha products on the market, and you’ll definitely want to start with just one capsule twice a day.  

Nootropics Depot is one of our preferred nootropics suppliers due to their expertise in nootropics manufacturing and sourcing.  They know how to get the best ingredients, make the best extracts, and their products are meticulously lab-tested.  


Toniiq’s ultra-concentrated ashwagandha extract capsules contain a whopping 10% withanolide content, which is 65 mg per capsule.  This is the single most potent ashwagandha product we’ve ever seen and offers incredible value for money.

This high dosage is of course very sedating– in fact, the recommended dosage is two capsules which contains 130 mg of withanolides!  As such, Toniiq ashwagandha is only recommended for pre-bed use. 

DailyNutra Ashwagandha

At 600 mg of KSM-66 ashwagandha per serving, DailyNutra is fairly potent and suitable for either pre-bed use, or people with a higher ashwagandha tolerance.  It also contains black pepper extract, which is an anti-inflammatory.  Since inflammation both impairs immune function and worsens your mood, the inclusion of black pepper extract is beneficial for both mood and overall health.  

Make sure to read our article on the best ashwagandha brands!

Ashwagandha FAQs

What is ashwagandha root extract good for?

Ashwagandha extract is primarily an anti-anxiety supplement.  Secondary to this, it is also an effective sleep aid and may increase thyroid function, testosterone levels in men, recovery from exercise, and modestly aid in weight loss.  

What can I take with ashwagandha?

Ashwagandha is safe to take with other supplements.  L-theanine in particular may have a synergistic effect, while low-dose caffeine can combine with ashwagandha for a relaxed, sustained energy boost.

You should talk to your doctor before combining ashwagandha with prescription drugs, however, especially anti-anxiety, anti-depressant, and sleep aid medications.

How does ashwagandha boost testosterone?

This is not entirely clear, but it is most likely a combination of improved sleep and reduced cortisol.  Since cortisol and testosterone are made from the same precursor hormone, pregnenolone, reducing the production of one allows for increased levels of the other.

How much ashwagandha can I take in a day?

600-900 mg of ashwagandha in total is the most you should usually take, but it depends on the withanolide content.  Limit your daily dosage to 45 mg of withanolides unless you are taking ashwagandha to treat severe insomnia.  

What is the best dosage for ashwagandha?

300 mg of ashwagandha, or 15 mg of withanolides, up to three times a day.  You can take a double dose before bed.  

What time of day do I take ashwagandha?

For sleep, before bed of course.  Otherwise, dosages are best split up throughout the day, morning, early afternoon, and evening.  Taking it on a full stomach will make the effect weaker but longer-lasting.  

What is the best type of ashwagandha?

KSM-66 ashwagandha is the best form of ashwagandha.  It is an extract of the root only and is standardized to 5% withanolides.  

What happens when you stop taking ashwagandha?

The effects seem to take a few days to wear off.  Beyond that, there is no sign that ashwagandha withdrawal occurs.  

What is KSM-66® ashwagandha?

It is a high-quality extract of only the root of the ashwagandha plant.  It’s standardized at 5% withanolide content for high potency.  

How long should you take ashwagandha for?

As long as you need to.  There are no indications that tolerance build-up occurs.  However, studies have rarely lasted more than two months, so you may want to take a two-week tolerance break every two or three months.  

How does ashwagandha affect the thyroid?

It may mildly increase thyroid hormone production, at least in cases of subclinical hypothyroidism.  This effect is very minimal and has not yet been confirmed by multiple studies.  It is not strong enough to treat clinical hypothyroidism. 

What side effects does ashwagandha have?

The only known side effects are drowsiness, and sometimes dizziness, from higher doses.  

Studies You Can Read About Ashwagandha

Editor’s note: we are regularly updating this review. If you see any problems, weird interpretations of the data, or just want to say hi, please reach out to

Photo by Keegan Houser on Unsplash

About the author

John Fawkes is the Managing Editor of The Unwinder. John is an NSCA-certified personal trainer and Precision Nutrition-certified nutritional counselor who has been featured on over two dozen websites and podcasts. He works with clients in Los Angeles and online, and can be reached on Instagram and Twitter.

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