Ashwagandha is one of the most popular ingredients in men's health and stress supplements. It's also one of the most poorly understood, because the conversation almost never gets past "total withanolides."
That label number tells you something. It just doesn't tell you what you probably think it tells you.
This piece walks through what withanolides actually are, why their form matters more than their total amount, what a 2023 peer-reviewed pharmacokinetic study showed about how different ashwagandha extracts behave in the bloodstream, and what to look for if you actually care about the difference between a supplement working and a supplement looking like it should work.
No product pitches. Just the science, and an honest look at how the supplement industry markets this ingredient.
What withanolides actually are
Ashwagandha (Withania somnifera) is a plant. The compounds in the plant that researchers believe drive its effects on stress, sleep, and hormonal markers are called withanolides. There are over 40 known withanolides in the plant, with names like withaferin A, withanolide A, withanolide D, and withanoside IV.
Every ashwagandha supplement on the shelf tells you what percentage of its extract is withanolides. You'll see "2.5% withanolides," "5%," "35%," or sometimes a proprietary number tied to a specific branded extract.
Most consumers stop there. Higher percentage equals more potent, right?
It's more complicated than that, and the science increasingly says the percentage on the label isn't the right number to look at.
The form is the missed variable
Withanolides exist in two structural forms in the plant: as aglycones (free withanolides) and as glycosides (withanolides bound to a sugar molecule).
Most commercial ashwagandha extracts on the market are rich in aglycones and contain only trace amounts of glycosides. The extraction processes that most manufacturers use favor aglycones because they're easier to concentrate. Aglycones are also what most ashwagandha research has historically measured.
The problem: aglycones have notoriously poor bioavailability and short plasma half-lives in humans. They appear in the bloodstream briefly and clear out fast. Researchers have known this for years. A 2013 mouse study and a 2022 toxicology paper both documented how quickly free withaferin A and withanolide A clear from the bloodstream after dosing.
Glycosides behave differently. They tend to be absorbed more efficiently and retained longer. This isn't unique to ashwagandha. Across many plant compounds, glycoside forms often show better bioavailability than their free aglycone counterparts because of how the gut handles them.
So if you're taking a supplement standardized to total withanolides without knowing what form those withanolides are in, you might be getting a high number on the label and a low number actually reaching your tissues.
The 2023 pharmacokinetic study on Shoden®
In 2023, researchers published a peer-reviewed pharmacokinetic study in Heliyon that directly compared two ashwagandha extracts in human plasma. The high-glycoside extract used was Shoden®, a branded ashwagandha standardized to 35% withanolide glycosides, manufactured by Arjuna Natural.
The design was rigorous for this kind of work. Randomized, double-blind, single-dose, crossover, 16 healthy adults (15 completed), 7-day washout between doses. Plasma withanolides were measured by LC-MS/MS, which is the gold standard for this kind of measurement.
The design choice that mattered
The researchers dosed both extracts to deliver an equal 185 mg of total withanolides. They did this on purpose to isolate the variable that mattered: not how much withanolide was being delivered, but in what form.
- Shoden® (the high-glycoside extract) required 480 mg of capsule contents to deliver 185 mg of total withanolides.
- The conventional 2.5% extract required 7,400 mg of capsule contents to deliver the same 185 mg.
Both groups got the same total withanolide payload. The question was whether the form of those withanolides mattered for what actually showed up in the bloodstream.
The results, comparing Shoden® to the conventional 2.5% extract on total withanolides in plasma:
About 18 times higher total exposure in plasma (AUC).
About 5.6 times higher peak concentration (Cmax).
About 4 times longer mean residence time in the body.
About 5 times longer half-life.
The two products were formally found not bioequivalent. The 90% confidence intervals fell well outside the standard bioequivalence range, which means the difference wasn't statistical noise.
There's a per-milligram normalization in the study that comes out to a much larger number (around 280x), but that figure is dose-normalized in a way that's easy to misuse in marketing. The honest interpretation of the per-milligram math is "when you compare equal weights of extract, Shoden® delivers dramatically more bioavailable withanolide than the 2.5% material." The 18x total exposure figure is the more practical number for consumers.
One disclosure worth making: a study author is affiliated with Arjuna Natural, the manufacturer of Shoden®, and has a related patent pending. This doesn't invalidate the data, but it's worth naming. Peer-reviewed publication in an independent journal still provides a meaningful credibility check, and the methodology was strong, but readers deserve to know the relationship exists. The supplement industry rarely names these conflicts. We're naming it because it matters.
Foundation uses 120 mg of Shoden®.
For transparency: that's why this piece is being written by us. The clinical research lined up before the formulation did.
What this means in practice
If you're picking an ashwagandha supplement, the questions to ask are:
What total withanolide percentage is the extract standardized to?
What percentage of those withanolides are glycosides versus free aglycones?
If the second question can't be answered by the manufacturer, that's information.
Most supplements that say "ashwagandha" or even "ashwagandha extract" don't disclose form. They just list a milligram amount and sometimes a withanolide percentage. The form question goes unasked because asking it forces a more complicated and less marketable answer.
The extracts with high glycoside content tend to be branded. Shoden® is the one with the strongest published pharmacokinetic data behind that claim, standardized to 35% glycosides. The branded designation isn't marketing fluff in this case. It tracks to a specific extraction process and a specific standardization that's been measured against pharmacokinetic outcomes in independent research.
On the broader research picture
There's also some additional manufacturer-internal data on longer-duration outcomes (like 60-day testosterone studies on Shoden®) that hasn't yet been peer-reviewed. Some of that data shows even stronger effects than the published Murdoch University crossover trial (which showed a 14% testosterone improvement at 120mg over 8 weeks in men).
We'll be honest about this: unpublished manufacturer data isn't the same as peer-reviewed evidence. It might be valid. It might not have made it through peer review yet for reasons that have nothing to do with quality. It might be a smaller pilot study not designed for publication. The men reading this who pay attention to the broader conversation about research integrity already know that peer review is an imperfect filter. Plenty of good science gets buried. Plenty of bad science gets through. We're not going to pretend the published literature is the only signal that matters.
What we will say is this. The published data on Shoden® is genuinely strong by ashwagandha-research standards. The mechanistic story (glycosides absorb better than aglycones) is supported across the literature on plant compound bioavailability generally. The internal data Arjuna has shared, where it exists, points in the same direction as the published data, which is a coherence check rather than proof.
Take that for what it's worth. Make your own call about how much weight to give each data source. That's the honest version of how supplement science actually works.
A few clarifications worth making
This piece is about extract bioavailability, not about whether ashwagandha "works." Whether ashwagandha is the right ingredient for your specific situation, at any dose, in any form, is a different question that depends on your goals, your baseline, and what else you're doing.
The 14% testosterone improvement from the Murdoch crossover study (Lopresti et al., American Journal of Men's Health, 2019) is a real published number, but it was a specific population (aging, overweight males) at a specific dose (120mg of Shoden®) over a specific duration (8 weeks). Generalizing it to "ashwagandha boosts testosterone X%" oversimplifies the data.
Ashwagandha isn't a stimulant or a hormone. It's an adaptogenic plant compound that the research suggests works on stress and cortisol pathways, with downstream effects that can include testosterone modulation in men with elevated stress and certain baseline conditions. The mechanism matters. The "boost your T" framing the supplement industry uses obscures the actual biology.
The bottom line
Most ashwagandha supplements market themselves on total withanolide percentage. The research increasingly says that's not the variable that determines what actually reaches your bloodstream.
Withanolide form matters. Glycosides absorb better and stay in the bloodstream longer than free aglycones. A peer-reviewed pharmacokinetic study in 2023 showed about 18 times higher total plasma exposure from Shoden® (standardized to 35% glycosides) compared to a conventional 2.5% extract, even when both delivered the same total withanolide dose.
If you're shopping for ashwagandha, ask about form, not just percentage. Most labels won't tell you. That itself is information.
Read the form, not the percentage.
---
Sources: Heliyon, 2023 (peer-reviewed PK study on Shoden® vs. conventional 2.5% ashwagandha extract). Lopresti et al., American Journal of Men's Health, 2019 (Murdoch University testosterone crossover, conducted with Shoden®). Lopresti et al., Sleep Medicine, 2020 (sleep). Additional manufacturer data referenced from Arjuna Natural's Shoden® clinical/PK materials. Mouse and toxicology background on aglycone elimination: J. Pharm. Biomed. Anal., 2013, and Toxicology Reports, 2022. Shoden® is a registered trademark of Arjuna Natural.
This article is educational. It is not medical advice. Always consult a qualified healthcare provider before changing your supplement routine, especially if you have any underlying health conditions or are taking medications. Statements about specific ingredients have not been evaluated by the FDA. No supplement is intended to diagnose, treat, cure, or prevent any disease.