Guide
Can you take milk thistle with vitamin K2?
No trial has tested milk thistle and vitamin K2 taken together. Vitamin K2 has a well-known interaction with blood-thinning medication that has nothing to do with milk thistle; that's the one caution worth flagging here.
No trial has tested milk thistle and vitamin K2 together as a supplement combination. The one interaction worth actually knowing about here isn't between the two of them — it's between vitamin K2 (any form) and blood-thinning medication like warfarin, which is a documented interaction that has nothing to do with milk thistle.
What each one is
Vitamin K2 is a fat-soluble vitamin involved in blood clotting and, separately, calcium regulation in bone and blood vessels. Milk thistle is a plant extract standardized to silymarin, with no established RDA; its own research is covered in milk thistle benefits: what the research does and doesn't show, and it was studied entirely in people already diagnosed with a liver or kidney condition.
The interaction that actually matters: K2 and blood thinners
Vitamin K (in any form, including K2) plays a direct role in the same clotting pathway that warfarin and similar blood-thinning medications work against, which is why NIH's Office of Dietary Supplements flags vitamin K intake, including from supplements, as something to keep consistent and discuss with a doctor if you're on that kind of medication. That caution applies to vitamin K2 on its own — it isn't specific to combining it with milk thistle.
Is there a milk thistle-specific interaction?
Milk thistle's own interaction research is small and separate from the vitamin K caution above: one human trial found a genotype-dependent effect on a blood-pressure medication's levels, and a separate trial found no significant effect on four major drug-processing liver enzymes. Neither trial, nor any other research we found on milk thistle, tested or flagged an interaction with vitamin K2 specifically. See milk thistle and medications: what to check for what that research does cover. If you're on a blood thinner, both the vitamin K2 caution above and milk thistle's own interaction profile are worth raising with a doctor together.
Why nattokinase comes up in the same search
Some combination products pair milk thistle with vitamin K2 and nattokinase, an enzyme sold as its own supplement ingredient. That's a formulation choice based on marketing category, not a tested claim — no trial has tested milk thistle, K2 and nattokinase together as a three-ingredient combination. Nattokinase's own evidence isn't covered on this page.
Questions people ask
Can you take milk thistle with vitamin K2?
No trial has tested the combination directly, and nothing in milk thistle's own research documents a conflict with vitamin K2. If you take a blood thinner, the relevant caution is about vitamin K2 itself, not milk thistle — talk to a doctor before adding either.
Does milk thistle affect vitamin K2, or the reverse?
No research we found measures that specifically. The two are chemically and functionally unrelated, so there's no known mechanism by which one would be expected to change the other, but "no known mechanism" isn't the same as a trial confirming no interaction.
Related reading: milk thistle and medications: what to check, who should not take milk thistle, and milk thistle benefits: what the research does and doesn't show.
Sources
- Effect of silymarin on the pharmacokinetics of losartan and its active metabolite E-3174 in healthy Chinese volunteers A 2009 trial found that 420 mg/day of silymarin for 14 days changed losartan blood levels in healthy volunteers, but the effect depended on the person's CYP2C9 genotype.
- Milk Thistle An NIH reference monograph reports no valid clinical trial support for milk thistle increasing milk supply, describes it as generally well tolerated with occasional GI/skin side effects, and flags rare but real allergic cross-reactivity with ragweed-family plants.
*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.