Milk Thistle (Silymarin)
Also known as: Silymarin, Silibinin, Silybin, Silybum marianum, Legalon
Lower numbers = closer to natural. Higher numbers = more enhanced.
Why this rating?
Milk thistle (silymarin) is a plant-extract supplement taken for liver support. It does not build muscle, alter hormones, or enhance performance. Rated 1 as a basic herbal supplement. Note the clinical evidence for meaningful liver benefit is mixed and generally weak.
Overview
Milk thistle is the common name for Silybum marianum, whose seed extract is silymarin, a standardised mixture of flavonolignans (silibinin/silybin, isosilibinin, silychristin, silidianin and others), of which silibinin is the major active constituent. It is one of the most popular liver-support supplements and is commonly run on-cycle alongside oral (17-alpha-alkylated) steroids. Honest caveat: for most liver conditions the clinical evidence is mixed and limited.
Purpose & Use Cases
General Liver Support
Taken as antioxidant/hepatoprotective support, especially by people using oral steroids or otherwise stressing the liver.
On-Cycle with Orals (Community Use)
Frequently stacked with 17-alpha-alkylated oral steroids as part of a liver-support protocol, often alongside TUDCA and NAC.
Amanita Poisoning (Medical, IV)
Intravenous silibinin (Legalon) is approved in Europe for death-cap mushroom poisoning; available in the US only via expanded-access IND.
Benefits
- Popular, well-tolerated herbal liver-support supplement
- Silibinin is a genuine antioxidant flavonolignan
- IV silibinin (Legalon) is an approved antidote for Amanita poisoning in Europe
- Widely used on-cycle alongside oral steroids
Good to Know
Silymarin vs silibinin: what you are actually taking
Milk thistle seed extract is silymarin, a standardised mix of flavonolignans; silibinin (silybin) is its major active constituent. Supplements are usually standardised to a percentage of silymarin (commonly 70-80%). Silibinin's bioavailability is poor, which is why "enhanced" phospholipid-complex versions exist.
The evidence is weaker than its popularity suggests
A Cochrane meta-analysis (13 RCTs, 915 patients with alcoholic and/or viral-hepatitis liver disease) found silymarin had no significant effect on all-cause mortality or complications; an apparent reduction in liver-related mortality when pooling all trials vanished in the highest-quality, low-bias trials. A dedicated JAMA-published RCT (Fried et al. 2012) also found high-dose silymarin (420-700 mg 3x/day) produced no significant improvement in ALT or HCV viral load versus placebo in treatment-resistant hepatitis C. Treat it as low-risk support, not a proven hepatoprotectant.
The one strong, approved use is mushroom poisoning
The best-established clinical use is intravenous silibinin (Legalon), approved in Europe as an antidote for Amanita (death-cap) mushroom poisoning, a very different context from an oral supplement capsule taken on cycle.
Dosage Guidelines
| Experience Level | Dosage Range |
|---|---|
| Beginner | 140 – 200 mg/day |
| Intermediate | 200 – 420 mg/day |
| Advanced | 420 – 600 mg/day |
Common supplement products are standardised to ~70-80% silymarin and dosed a few hundred mg/day. The ranges here reflect that community practice, not a validated clinical dose. Oral bioavailability of silibinin is poor; phospholipid-complex formulations (e.g. Siliphos) are reported far more bioavailable. A phase I oncology trial found doses as high as 13 g/day well tolerated (with mild liver-enzyme elevation), so the safety margin is wide even if efficacy is uncertain.
Elimination half-life is roughly 6-8 hours; oral bioavailability of silibinin is low.
Side Effects
GI upset
uncommonMild bloating, nausea or loose stools.
Take with food.
Mild liver-enzyme elevation (high doses)
rareNoted as the main adverse effect at very high (multi-gram) doses in a phase I trial.
Not relevant at normal supplement doses.
Allergy (Asteraceae family)
rarePeople allergic to ragweed/daisies/marigolds (Asteraceae) may react.
Avoid if allergic to related plants.
General Mitigation Strategies
Milk thistle is very well tolerated, even multi-gram doses were tolerated in a phase I trial. Take with food. The honest limitation is efficacy, not safety: do not rely on it to make oral steroids safe. Dose/duration limits, avoiding unnecessary orals, and bloodwork are the real liver protection.
Support Supplements
Ancillary supplements commonly run alongside Milk Thistle (Silymarin) to manage side effects, support the target tissue, or fill nutrient demands it creates.
TUDCA
TUDCA has more direct rationale for oral-steroid liver support (it supports bile flow and counters cholestasis, which is the main way 17-alkylated orals damage the liver). Milk thistle is often added on top as antioxidant support.
- Dose
- TUDCA 500-1,000 mg/day; milk thistle a few hundred mg/day silymarin
- Timing
- Through the oral portion of the cycle, with meals
- When
- If prioritising evidence, TUDCA (and dose/duration limits) matter more than milk thistle for oral-steroid protection.
Post Cycle Therapy (PCT)
Not hormonal. Does not affect the HPTA. No PCT required.
How It Works
Silymarin's flavonolignans (chiefly silibinin) are proposed to act as antioxidants, stabilise hepatocyte membranes and support liver-cell function. The one well-established clinical use is intravenous silibinin (as the dihemisuccinate, trade name Legalon) for Amanita (death-cap) mushroom poisoning, approved in Europe for that indication. For everyday oral supplement use the hepatoprotective mechanism is far less firmly demonstrated in humans.
Fundamentals
Reference on the practices relevant to Milk Thistle (Silymarin): how they are done and where they go wrong. Not a recommendation to use it.
Legal Status
OTC dietary supplement (USA); IV silibinin (Legalon) is approved in Europe for Amanita poisoning.
Legal status varies by country and changes over time. This is a general summary, not legal advice.
WADA Status
Milk thistle / silymarin is not on the WADA Prohibited List. It is a herbal dietary supplement with no hormonal or performance-enhancing action.