Research review
Does milk thistle help with stress? What the research does and doesn't show
No human trial has tested milk thistle for everyday stress or measured its effect on cortisol. The one placebo-controlled trial that tracked anxiety and depression as outcomes, in adults with gambling disorder, found silymarin performed no differently than placebo.
The evidence doesn't support milk thistle as a calming supplement or a way to lower cortisol. The one placebo-controlled human trial that measured anxiety and mood as outcomes — in adults with gambling disorder, not stress — found silymarin performed no differently than placebo on any measure, including anxiety and depression scores.
What the evidence doesn't support
It doesn't support milk thistle for everyday stress, as a "calm" supplement, or as a way to lower cortisol — no trial has measured milk thistle's effect on cortisol in a person at all. It also doesn't support milk thistle as a treatment for anxiety: the one placebo-controlled human trial that tracked anxiety as an outcome found no difference between silymarin and placebo.
What the trials found
A 2024 double-blind, placebo-controlled trial gave 43 adults with gambling disorder silymarin (150–300 mg twice a day) or placebo for 8 weeks. The main outcome was a gambling-symptom scale, but the study also tracked depression and anxiety measures as secondary outcomes. Silymarin did not statistically differentiate from placebo on any outcome measure — gambling symptoms, depression, or anxiety. Both groups improved substantially (a 56–57% reduction in gambling-symptom scores), which the authors attribute to a large placebo response rather than a drug or supplement effect. This is the only placebo-controlled human trial we found that measured mood or anxiety alongside silymarin.
A 2023 systematic review pooled 17 studies looking at silymarin and silibinin's effects related to depression and anxiety. It reports that silymarin and silibinin raised markers like brain-derived neurotrophic factor and several neurotransmitters, and lowered markers of oxidative stress and inflammation, in the studies it reviewed. The review's own methods section doesn't specify how many of the 17 studies were in humans versus animals, and its cited mechanisms — neurotransmitter levels, inflammatory markers, brain tissue changes — are the kind of measurements typically taken in animal or lab studies, not human trials of mood. The review concludes silymarin and silibinin "can be used" for depression and anxiety, while also stating more clinical studies are needed — a conclusion this page doesn't adopt, given the one human, placebo-controlled trial above found no effect.
Separately, several animal studies have tested silymarin or silibinin in rodent models of induced stress — restraint stress and prolonged-stress protocols in mice and rats, and models of post-traumatic stress in mice — and reported changes in stress-related behavior and brain chemistry. These are laboratory models of physically or psychologically stressing an animal, not studies of a person's everyday stress, and none of them used silymarin alone as a human-comparable supplement dose.
No trial, in animals or humans, has measured milk thistle's or silymarin's effect on cortisol.
| Study | Design | Population | Result |
|---|---|---|---|
| Gambling disorder trial, 2024 | Double-blind, placebo-controlled, 8 weeks | 43 adults | No difference from placebo on gambling, depression or anxiety scores |
| Depression/anxiety review, 2023 | Systematic review of 17 studies, mostly mechanistic | Not specified (largely animal/lab) | Reports biological mechanisms; not a human trial result |
| Rodent stress models | Various animal studies | Mice and rats | Behavioral/biochemical changes in induced-stress models |
Questions people ask
Does milk thistle lower cortisol?
No trial has measured this in a person, or in an animal. There's no research to answer this either way.
Is milk thistle good for stress?
There's no human trial testing milk thistle against everyday stress. The closest human data — a placebo-controlled trial that tracked anxiety and depression as secondary outcomes — found no effect from silymarin.
Can milk thistle help with anxiety?
The one placebo-controlled human trial that measured anxiety found silymarin performed no differently than placebo. A 2023 review reports that silymarin affects stress-related brain chemistry in mostly animal and lab research, but that's a different, weaker kind of evidence than a clinical trial result in anxious people.
Does milk thistle have a calming or sedative effect?
No human trial has tested milk thistle for a calming or sedative effect. The gambling-disorder trial above, which tracked mood outcomes most closely to this question, found no difference from placebo.
When to talk to a doctor
Stress or anxiety that's persistent, or that interferes with sleep, work or daily life, is worth discussing with a doctor, who can evaluate other causes and discuss options with an established evidence base. Milk thistle is not a treatment for stress, anxiety or elevated cortisol, and the one relevant human trial found no effect. If you take medication for anxiety or any other condition, talk to a doctor before adding a supplement.
Related reading: milk thistle: what the research does and doesn't show, milk thistle side effects, and milk thistle benefits.
Sources
- Silymarin (Milk Thistle) Treatment of Adults With Gambling Disorder: A Double-Blind, Placebo-Controlled Trial In a placebo-controlled trial of 43 adults, silymarin (300–600 mg/day) performed no differently than placebo on gambling, depression, or anxiety scores over 8 weeks — both groups improved similarly, which the authors credit to a placebo effect.
- The Therapeutic Effect of Silymarin and Silibinin on Depression and Anxiety Disorders and Possible Mechanism in the Brain: A Systematic Review A systematic review of 17 studies reports that silymarin and silibinin affect stress-related brain chemistry (neurotransmitters, inflammation, neurogenesis) — measures typical of animal and lab research, not a human clinical trial outcome — and its own authors say more clinical studies are needed.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.