Milk thistle vs ashwagandha: what the research does and doesn't show

Milk thistle and ashwagandha have been studied for almost entirely different things — milk thistle's trials sit in people already diagnosed with a liver or kidney condition, ashwagandha's mainly in stress and cortisol in otherwise healthy adults. No trial has tested them against each other, so "which is better" doesn't have a research-backed answer either way.

What the evidence doesn't support

It doesn't support ranking one above the other for the same outcome, because they haven't been tested for the same outcome. It doesn't support using ashwagandha's stress trials to say anything about milk thistle, or milk thistle's liver and kidney findings to say anything about ashwagandha. And it doesn't support treating either one as a treatment for a diagnosed liver or kidney disease, or for a stress or anxiety condition — that's not what either evidence base shows.

What the trials found

Milk thistle's human evidence was run entirely in people already diagnosed with a liver or kidney condition. A 2017 pooled analysis of 6 trials in people with diagnosed liver disease found silymarin lowered ALT and AST by a statistically significant but, in the authors' own words, clinically negligible amount. A 2024 pooled analysis of 26 trials specifically in nonalcoholic fatty liver disease (NAFLD/NASH) found larger improvements — in lipid markers, liver enzymes and, in a subset with biopsy data, liver histology — but the authors called for further confirmation. On the kidney side, a small 2012 trial in 60 people with diabetic kidney disease found 420 mg/day of silymarin for 3 months reduced a urine-protein marker more than placebo. A separate 2021 systematic review found silymarin's active compounds are poorly absorbed orally, a limitation that sits under all of the findings above. None of milk thistle's trials measured stress, anxiety or cortisol.

Ashwagandha's evidence sits in a different domain. A 2012 randomized, placebo-controlled trial gave 64 adults with a history of chronic stress 600 mg a day of a concentrated ashwagandha root extract for 60 days and found significantly lower stress-scale scores and cortisol than placebo. A 2024 meta-analysis pooling 9 trials, 558 people total, found ashwagandha outperformed placebo on stress and anxiety-scale scores and on cortisol, though doses varied across the pooled trials. None of ashwagandha's stress trials measured liver enzymes or kidney function.

No trial has given people milk thistle and ashwagandha together, and no trial has put the two head-to-head on the same outcome. Whatever each literature suggests about its own domain, there's no dose-matched or head-to-head evidence for choosing between them.

Ingredient	Best evidence	Population	Dose in that trial
Milk thistle	Mixed: negligible liver-enzyme change in a 2017 pooled analysis; larger NAFLD-specific improvements in a 2024 pooled analysis; a positive kidney-marker result in one small trial	Adults already diagnosed with liver or kidney disease	420 mg/day silymarin (where reported)
Ashwagandha	Lower stress-scale scores and cortisol vs. placebo, confirmed across a 9-trial meta-analysis	Adults with chronic stress	600 mg/day, 60 days (in the RCT); varied across the pooled meta-analysis trials
Both together	No trial exists	—	—

Questions people ask

Which is better, milk thistle or ashwagandha?

They haven't been tested for the same thing, so there's no trial to answer "better" either way. Milk thistle's evidence is about liver and kidney markers in people with a diagnosed condition; ashwagandha's is about stress-scale scores and cortisol in people with chronic stress.

Can you take milk thistle and ashwagandha together?

No trial has tested the combination, so there's no evidence describing what taking them together adds beyond either alone. Ashwagandha should be discussed with a doctor if you're pregnant or nursing, have a thyroid condition, or take other medication; milk thistle has its own interaction profile, covered in milk thistle and medications: what to check.

Is ashwagandha better than milk thistle for stress?

Ashwagandha has the established stress and cortisol evidence of the two — none of milk thistle's trials measured stress, anxiety or cortisol at all.

Is milk thistle better than ashwagandha for the liver?

Milk thistle is the one with liver-specific human trials, though the results are mixed: modest at best in a general liver-disease population, more promising but still unconfirmed in NAFLD/NASH specifically. Ashwagandha's trial base doesn't include liver-marker outcomes.

When to talk to a doctor

Diagnosed liver disease, kidney disease, or a stress-related condition all call for medical guidance rather than a supplement search. Neither milk thistle nor ashwagandha is a treatment for any of those, and the trials above were run alongside, not instead of, standard medical care. Ashwagandha should be discussed with a doctor if you're pregnant or nursing, have a thyroid condition, or take other medication; milk thistle's own interaction evidence, while limited, is a reason to check in before combining it with a prescription.

Related reading: milk thistle benefits: what the research does and doesn't show, milk thistle and medications: what to check, and how much milk thistle should you take a day.