Supplement analysis backed by scientific evidence · PT

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Limited evidenceGeneral health

Rehmannia

Rehmannia glutinosa is a foundational "kidney yin" herb in Chinese medicine and is almost never studied alone — the human evidence is for multi-herb formulas like Rehmannia-6 (Liu Wei Di Huang Wan), where results are modest and the herb's individual contribution is unknown. As a standalone Western supplement it is essentially untested.

What the science says

  • Rehmannia-6 formula showed modest kidney benefit in type 2 diabetes, but that is a six-herb formula Moderate evidence

    A multicenter RCT (n=148) added a Rehmannia-6-based Chinese herbal formula to standard care in adults with type 2 diabetes and stage 2-3 chronic kidney disease for 48 weeks. The herbal arm showed a smaller decline in eGFR and improved symptom scores versus placebo, with acceptable safety. This is genuine evidence for the formula, not for isolated rehmannia — the same formula contains dioscorea, cornus, poria, alisma and moutan bark.

  • Catalpol and rehmannia polysaccharides are pharmacologically active in animals only Limited evidence

    Reviews catalog anti-inflammatory, neuroprotective, hypoglycemic and immunomodulatory effects of catalpol (the signature iridoid glycoside) and Rehmannia polysaccharides in rodents and cell culture. Catalpol has poor oral bioavailability (single-digit percent in animal pharmacokinetic studies), which makes extrapolation from injected-animal doses to oral human supplements unreliable.

  • No credible standalone evidence for adrenal support, anti-aging, or autoimmune claims Limited evidence

    Marketing positions rehmannia as an "adrenal restorative" and a corticosteroid-sparing herb. There are no placebo-controlled human trials of rehmannia alone for cortisol, fatigue, or autoimmune disease outcomes; the steroid-sparing idea comes from small uncontrolled Chinese reports of combination formulas.

Dosage & safety

Studied doseTraditional decoctions use 9-30 g/day of prepared root (shu di huang) or 9-15 g/day of the raw/dried root (sheng di huang), always within a formula. Western capsules typically supply 400-1,000 mg of dried root or a 5:1 to 10:1 extract, far less than decoction doses. Formula trials such as Rehmannia-6 dose the whole granule preparation, not a fixed rehmannia amount, so no isolated evidence-based dose exists.
SafetyGenerally well tolerated. The most common complaints are digestive: loose stools, bloating, and reduced appetite, which is why classical formulas pair it with digestion-supporting herbs. Raw rehmannia is considered "cold" and more likely to cause diarrhea than the prepared form. Theoretical additive effects with blood-glucose-lowering drugs — monitor if you are on insulin or sulfonylureas. Avoid in pregnancy due to absent data. As with all Chinese herbal imports, adulteration and heavy-metal contamination have been documented in the wider category; buy from suppliers who publish third-party testing.

Scientific references

Where to buy

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