Rehmannia is one of the most-used roots in Traditional Chinese Medicine (TCM), where it almost always appears inside formulas rather than on its own. It comes in two processed forms with different uses, and it has a large body of lab research. What it does not yet have is much human trial evidence, and that gap is important to understand before using it.
What is rehmannia?
Rehmannia is the root of Rehmannia glutinosa, sometimes called Chinese foxglove. A 2008 review identified more than 70 compounds in the root, including iridoid glycosides (catalpol is the most studied) and phenylethanoid glycosides such as acteoside. The same review notes the plant has been studied for effects on the blood, immune, hormonal, heart, and nervous systems, mostly in lab and animal work (Zhang et al., 2008).
Raw vs prepared rehmannia
The single most useful thing to know is that rehmannia comes in two forms, and processing genuinely changes its chemistry.
- Sheng Di Huang (raw rehmannia): the dried unprocessed root. In TCM it is considered cool and is used for patterns of heat and dryness. It keeps more of its original catalpol.
- Shu Di Huang (prepared rehmannia): the root steamed repeatedly, often with rice wine. In TCM it is considered warm and nourishing, used for fatigue and "deficiency" patterns.
This is not just tradition. A 2022 study confirmed that steaming breaks down catalpol and, through the Maillard reaction, creates new compounds such as 5-HMF, measurably changing the root's chemistry and antioxidant activity (Rahmat et al., 2022). So raw and prepared rehmannia are genuinely different products.
What the research actually shows
Most rehmannia research is preclinical, meaning it comes from cells and animals rather than people.
Catalpol: the most-studied compound
Catalpol, the main iridoid in raw rehmannia, has been reviewed for anti-inflammatory and nerve-protecting activity. In cell and animal models it lowers inflammatory signals such as TNF-alpha and IL-6 and protects neurons from oxidative stress (Yang et al., 2020). These are promising mechanisms, but they are not proof of benefit in humans.
Blood sugar: animal data only
Catalpol also shows blood-sugar-lowering effects in diabetes models. Crucially, a 2019 review of catalpol states plainly that there are "no clinical studies to examine its effects in humans" for diabetes; the diabetes evidence rests entirely on animal and cell research (Bhattamisra et al., 2019). So despite what some websites claim, there is no good human trial showing rehmannia treats type 2 diabetes. Do not use it as a substitute for diabetes care.
The honest bottom line
Rehmannia has interesting chemistry and a long traditional record, but strong human evidence that the single herb treats any specific disease is missing. It is almost always used within a formula, which makes single-herb claims even harder to support.
Traditional uses
In TCM, raw rehmannia is used within formulas for "heat" and dryness patterns, and prepared rehmannia for "blood and essence deficiency" patterns such as fatigue and weakness. It features in classic formulas like Liu Wei Di Huang Wan, where it is combined with several other herbs at set ratios (Zhang et al., 2008). These are traditional indications, not proven medical treatments.
Dosage and preparation
Rehmannia is almost always used in combination formulas, not alone. Practitioner-guided ranges within a formula are roughly:
- Raw (Sheng Di Huang): 10β15 g/day of dried root in decoction, sometimes higher under supervision.
- Prepared (Shu Di Huang): 9β30 g/day depending on the formula.
Because the form and dose are matched to a specific pattern, rehmannia is best used under a qualified TCM practitioner rather than self-prescribed.
Side effects and safety
- Digestive upset: loose stools, bloating, or mild nausea are the most reported effects, more so with raw rehmannia and in people with weak digestion.
- Diabetes medicines: because catalpol lowers blood sugar in animals, anyone on insulin or glucose-lowering drugs should check with their prescriber before use, to avoid an additive effect.
- Pregnancy and breastfeeding: safety is not established, so avoid it.
- Serious conditions: do not use rehmannia in place of treatment for diabetes, kidney disease, or any diagnosed illness. If you take prescription medicines, check for interactions first.
For background on using herbs and TCM safely, see NCCIH.
For other roots used in the same formulas, see our guides to white peony and bupleurum.
Frequently Asked Questions
What is rehmannia used for? In Chinese medicine it is used within formulas for "heat and dryness" patterns (raw form) or fatigue and "deficiency" patterns (prepared form). Human evidence for specific diseases is limited.
Does rehmannia lower blood sugar? Its compound catalpol lowers blood sugar in animal studies, but there are no human trials confirming this. Do not use it to manage diabetes on your own, and if you take diabetes medicines, ask your doctor first.
What is the difference between Sheng Di Huang and Shu Di Huang? Sheng Di Huang is raw rehmannia (cool, used for heat patterns); Shu Di Huang is steam-processed (warm, used for deficiency patterns). Steaming changes the chemistry, so they are used differently.
Can rehmannia be combined with white peony? Yes, they are often combined in classic formulas, but the right ratio and use should be set by a qualified practitioner.
Medical disclaimer: This article is for informational purposes only. Always consult a qualified healthcare provider before making changes to your health routine.
Sources
- Zhang RX, et al. Rehmannia glutinosa: review of botany, chemistry and pharmacology. Journal of Ethnopharmacology, 2008;117(2):199-214 β PubMed. https://pubmed.ncbi.nlm.nih.gov/18407446/
- Yang C, et al. Neuroprotective Effect of Catalpol via Anti-Oxidative, Anti-Inflammatory, and Anti-Apoptotic Mechanisms. Frontiers in Pharmacology, 2020 β PubMed Central. https://pmc.ncbi.nlm.nih.gov/articles/PMC7240050/
- Bhattamisra SK, et al. Multiple Biological Effects of an Iridoid Glucoside, Catalpol, and Its Underlying Molecular Mechanisms. Biomolecules, 2019 β PubMed Central. https://pmc.ncbi.nlm.nih.gov/articles/PMC7023090/
- Rahmat E, et al. Evaluation of Marker Compounds and Biological Activity of In Vitro Regenerated and Commercial Rehmannia glutinosa Roots Subjected to Steam Processing. Evidence-Based Complementary and Alternative Medicine, 2022 β PubMed Central. https://pmc.ncbi.nlm.nih.gov/articles/PMC9763011/
- National Center for Complementary and Integrative Health (NCCIH). Traditional Chinese Medicine: What You Need To Know. https://www.nccih.nih.gov/health/traditional-chinese-medicine-what-you-need-to-know
All sources accessed 29 May 2026.
