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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.

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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.

How to take it

TimingDivided doses across the day, traditionally as a decoction.
With food?With food; on its own it commonly causes loose stools, bloating and reduced appetite.
Worth knowingClassical practice never uses it alone — those digestive effects are exactly why formulas pair it with warming, digestion-supporting herbs.

Interactions

With medications

  • insulin, sulfonylureas and other glucose-lowering drugs

    Rehmannia may lower blood glucose and add to their effect. monitor your glucose when starting or stopping

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

What is rehmannia used for?

Rehmannia glutinosa is a foundational "kidney yin" herb in Chinese medicine that is almost always used inside multi-herb formulas such as Rehmannia-6 (Liu Wei Di Huang Wan). As a standalone Western supplement, rehmannia is essentially untested (limited evidence).

Does rehmannia help kidney function in diabetes?

A Rehmannia-6-based formula has moderate evidence: in a 48-week trial of 148 adults with type 2 diabetes and stage 2-3 chronic kidney disease, it slowed eGFR decline versus placebo when added to standard care. That is evidence for a six-herb formula, not for rehmannia alone.

Does rehmannia support the adrenals?

There are no placebo-controlled human trials of rehmannia alone for cortisol, fatigue or autoimmune disease (limited evidence). The adrenal and steroid-sparing claims come from small uncontrolled Chinese reports on combination formulas.

What are the side effects of rehmannia?

Rehmannia is generally well tolerated, but it commonly causes loose stools, bloating and reduced appetite, which is why classical formulas pair it with digestion-supporting herbs. It may add to glucose-lowering drugs, so monitor your glucose if you take insulin or sulfonylureas, and avoid it in pregnancy.

Scientific references

Where to buy

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