TUDCA vs Milk Thistle: Differences and Taking Both

TUDCA and milk thistle are different kinds of supplement: TUDCA is a bile acid your own liver makes in small amounts, while milk thistle is a plant extract. Both are sold for liver support and both have mostly been studied in people with liver disease, but we found no study in people that tested them together.

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Milk thistle has been one of the best-known liver supplements for decades, and TUDCA has become its newer rival on supplement shelves. Many product pages say they work "synergistically", and some capsules contain both. Before choosing one, or both, it helps to know what each is and what the research in people actually shows.

This guide compares the two side by side, sets out the evidence for each in plain terms, and covers what to know about taking them together. It is written for adults who have had their gallbladder removed, have been told their liver tests are raised, or simply want to look after their liver.

Milk Thistle vs TUDCA: What Is the Difference?

The difference starts with what they are. Milk thistle supplements are an extract of the seeds of a flowering plant [1], and the main ingredient is silymarin [2], a mix of related plant compounds whose main component is silybin, also called silibinin [3]. TUDCA is a bile acid, the taurine-bound form of ursodeoxycholic acid, that occurs naturally in small amounts in human bile [4, 5].

They are also studied in different ways. Milk thistle's silymarin is studied mostly for its effects on the liver cells themselves [3]. TUDCA is absorbed and joins the bile acids your body recycles, and in people with a liver condition it shifted the mix in bile toward the water-loving kind [6]. As a supplement, it is used to support healthy bile flow as well as the liver.

	Milk thistle	TUDCA
What it is	A seed extract (silymarin)	A bile acid your body makes in small amounts
Where it comes from	The milk thistle plant	Made in a lab for supplements
Studied in people for	Liver disease, including fatty liver	Liver conditions, gallstones, indigestion after gallbladder removal
What the research shows	ALT may fall in fatty liver (very low certainty); other liver trials conflicting or too limited	Liver enzymes fell in several trials in liver conditions, including one against placebo
Common side effects	Bloating, nausea, gas; allergy in some people	Mostly mild digestive effects, such as looser stools
Tested together in people	We found no study of the two together

What Does the Research Show for Milk Thistle?

Despite its popularity, the research on milk thistle in liver disease has not settled whether it helps. The National Center for Complementary and Integrative Health describes the trials in liver disease as conflicting or too limited, and notes that two studies it funded, in hepatitis C and in the inflammatory form of fatty liver disease, showed no benefit [2].

In fatty liver, a 2025 Cochrane review of 17 trials found that silymarin taken on its own may lower the liver enzyme ALT by about 7 U/L compared with placebo or no treatment, based on 6 trials in 409 people, while silymarin combined with other ingredients did not lower it [7]. The reviewers rated that evidence as very low certainty, which means the true effect is likely to be substantially different, and judged both the benefits and the harms unclear. An earlier Cochrane review in alcohol-related and viral liver disease found no significant effect on overall deaths, complications of liver disease or liver tissue [8].

The American Association for the Study of Liver Diseases lists silymarin among several well-studied options, including some prescription drugs, that should not be used as a treatment for the inflammatory form of fatty liver disease, because they do not offer a meaningful benefit to the liver tissue [9]. Even so, milk thistle appears in 19 of the 20 most popular liver cleanse supplements sold on Amazon [10].

What Does the Research Show for TUDCA?

TUDCA's research in people is also mostly in liver conditions, with smaller studies elsewhere. In a placebo-controlled trial of 150 people with chronic hepatitis C, liver enzymes fell more on TUDCA than on placebo over six months [11]. In primary biliary cholangitis, a chronic bile duct disease, it gave similar results on the main liver test to the standard prescription bile acid, although two other liver enzymes fell more on the prescription drug [12].

For fatty liver, TUDCA has not been tested as a treatment, and in a four-week trial liver fat did not change [13]. After gallbladder removal, one study of 203 people found indigestion eased faster on TUDCA than with no treatment in the first month, after which the untreated group caught up [14]. Our guide to TUDCA benefits sorts all the evidence by use.

Which Is Better, TUDCA or Milk Thistle?

Neither is better in general, because they are different things and no trial has compared them. The more useful question is what you want help with.

If you have had your gallbladder removed

Without a gallbladder, bile flows directly from the liver into the small intestine [15], and less bile acid reaches the gut in the first minutes of a fatty meal [16]. TUDCA is itself a bile acid that joins the bile acids your body recycles [6], and it has one study in people after gallbladder removal that measured indigestion [14]. Milk thistle has been given after gallbladder removal only in small studies that measured the makeup of bile, not how people felt after meals [17]. Dr.Primal's TUDCA is made for life after gallbladder removal and taken with meals, to support healthy bile flow and fat digestion when richer meals feel heavy.

If your liver tests are raised

Raised liver enzymes have many possible causes, from fatty liver and alcohol to medicines and hepatitis [18], and finding the cause matters more than choosing a supplement. Our guide to elevated liver enzymes explains the usual next steps.

If you want general liver support

Both have been studied mainly in people with liver disease [2, 11], so the research does not show what either does for a healthy liver. For fatty liver, the approaches that form the foundation of treatment are not supplements at all: a healthy diet and regular exercise, with weight loss for people who carry extra weight and no heavy drinking [9]. Our fatty liver diet guide covers them.

Can I Take TUDCA and Milk Thistle Together?

Many people do, and some products combine them, but we found no study in people testing TUDCA and milk thistle together. That means any benefit of the pair is unknown, and claims that they are "synergistic" describe a theory rather than a result.

We also found no reported interaction between them. The Italian TUDCA label does not list milk thistle among its interactions [5], and both are generally well tolerated on their own [1, 19]. If you want to try both, start one at a time, so you can tell which one is responsible for any change. Many people in online supplement and liver forums describe taking the two together, often alongside NAC, but personal reports can't tell you whether the combination adds anything.

What Not to Mix Milk Thistle With?

No clinically important drug interaction has been confirmed for milk thistle. Laboratory studies show it can affect the liver enzymes that process some medicines, but there is little evidence that this matters in people [1]. The National Center for Complementary and Integrative Health advises telling your health care providers about any supplement you use [2].

Milk thistle can cause allergic reactions, particularly in people who are allergic to related plants such as ragweed, chrysanthemum, marigold and daisy [2]. Its most common side effects are digestive: bloating, nausea and gas [2].

What Should You Not Take TUDCA With?

The Italian TUDCA medicine label advises keeping it two hours apart from bile acid binders such as cholestyramine and colestipol, and from aluminum-containing antacids [5]. It also says cyclosporine levels may need monitoring, and advises against taking TUDCA with estrogens, hormonal contraceptives, some cholesterol-lowering drugs and drugs that can harm the liver [5].

No study in people has been designed to test these interactions, so they are cautions rather than proven effects. If you take prescription medicines, ask your pharmacist how to fit either supplement around them. Our guide to when to take TUDCA covers timing.

Is TUDCA Hard on the Liver?

In trials, TUDCA was mostly given to people who already had liver conditions, and their liver enzymes generally fell rather than rose [11, 20]. In a placebo-controlled trial lasting a year, side effects were no more common with TUDCA than with placebo [19]. The Italian label advises against it with a blocked bile duct or an acute gallbladder or bile duct inflammation [5].

Any supplement can occasionally affect the liver, and signs such as yellowing skin or eyes, dark urine, unusual tiredness or itching should be checked by a doctor [21]. Our TUDCA safety review lists the side effects reported in the human studies of TUDCA.

What About TUDCA vs Milk Thistle vs NAC?

NAC is a third supplement often sold for the liver, and it is different again. In hospitals, NAC is given to prevent or limit liver injury after an acetaminophen overdose [22], which is a medical treatment, not something a supplement does. Small, short trials have tried NAC in fatty liver, such as one in which 30 people took NAC or vitamin C for three months [23], and it has not been tested as a way to protect a healthy liver. Our guide to liver health supplements compares NAC, milk thistle and others.

In Summary: TUDCA vs Milk Thistle

TUDCA and milk thistle are different supplements: a bile acid that joins your body's own bile, and a plant extract studied for its effects on liver cells. Both have been studied mainly in people with liver disease, milk thistle's trials have given conflicting results, and we found no study in people that tested the two together.

For someone without a gallbladder, TUDCA is the one of the two that is itself a bile acid. If you are working out what is behind your own symptoms after meals, our digestion quiz is a quick way to put your symptoms and habits in order.

This article is for general education and is not a substitute for advice from your doctor. TUDCA is sold as a dietary supplement. 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.