What is Rehmannia?
Rehmannia glutinosa is a flowering plant found in central China. It’s sometimes called Chinese foxglove because it looks somewhat like a foxglove flower, though the two aren’t actually related [1+].
According to the traditional outlook, the harmony of opposite, but complementary, forces – yin and yang – underlies good health. Rehmannia is thought to help with yin energy imbalances. It is traditionally used to fight bacterial infections, as a tonic, and for a variety of conditions associated with inflammation, like asthma and arthritis [4+, 5, 1+].
Rehmannia is also often combined with other herbs to remedy “yin deficiency”. For example, it’s one of the six ingredients in a popular Chinese herbal product called Rehmannia Six Formula and one of the seven ingredients in the traditional kidney-nourishing herbal formulation Yukmi-jihang-tang. It is also included in widely-used formulations, such as Liuwei Dihuang Pills [6, 3, 7].
- May decrease fatigue and improve endurance
- May improve kidney and bone health
- May help fight cancer
- May be beneficial for diabetes
- May balance mood and the negative effects of stress
- Unclear which active components are responsible for the benefits
- Researched and often used in multi-herb formulations
- Weak or low-quality evidence for many benefits
- Side effects largely unknown
Depending on how the roots are prepared, they are called [10+]:
- Xian-Di-Huang (for the fresh root)
- Sheng-Di-Huang (for baked roots)
- Shu-Di-Huang (for steamed roots) in Chinese
Over 70 active compounds have been found in Rehmannia, including amino acids, simple and complex sugars, vitamins, and plant-specific compounds. Their composition in extracts mostly varies according to the plant species and the root preparation method [5, 9].
One of the most well-known plant-specific compounds in Rehmannia is called catalpol, which accounts for 0.3-0.5% of the dried root. Catalpol is an iridoid glycoside, a group of molecules plants create to defend against predators. They also have a range of health effects in humans [1+, 11, 12+].
Catalpol is likely responsible for the plant’s sugar-lowering, inflammation-fighting, and immune-balancing benefits. Rehmannia also contains rehmapicrogenin, a strong anti-inflammatory. This compound that helps deactivate one of the most important inflammation-triggering factors in the body (NF-κB) [13+, 14].
How Does Rehmannia Work?
Rehmannia may improve stress resilience and mood by enhancing the body’s antioxidant defense .
Certain complex sugars in Rehmannia may also protect the hippocampus – a part of the brain that plays an important role in memory and mood. Catalpol might also help brain cells resist damage. As a result, the plant’s compounds might prevent or improve dementia and anxiety [16, 17, 11].
Rehmannia also affects energy use and may be beneficial for people with diabetes and insulin resistance. Sugar extracts of this plant increased insulin production in mice and catalpol lowered glucose levels in diabetic rats. Catalpol also increases the secretion of endorphins from the adrenal gland, which helps transport glucose from the blood into the muscles [18, 19+, 20, 21].
This Chinese herb may help reverse anemia by protecting parts of the bone marrow that make red blood cells. Nourishing the blood is one of its main traditional indications, while anemia is considered to be a sign of yin deficiency. Eager to confirm the benefits, early sickle-cell anemia clinical trials are in progress with a compound isolated from the steamed roots [22, 23].
Rehmannia may help to alleviate inflammation by sponging up free radicals – highly reactive compounds that can damage cells – as well as by causing immune cells to secrete fewer inflammatory signaling molecules. Importantly, it also blocks the expression of inflammatory genes. Reducing inflammation, in turn, can be beneficial for bone and kidney health [14, 24, 25, 26, 27, 28+].
What’s more, this herb may cause kidney cells to express fewer receptors that drive high blood pressure. This is important for protecting the kidneys that are already strained due to other diseases, like diabetes. Dried and steamed roots reduce renin, which helps lower blood pressure and reduces kidney damage [28+, 29+].
Rehmannia may activate cancer-fighting immune cells. Additionally, it may cause cancer cells to express proteins that slow their growth. Its strength may lie in its lack of drug interactions or even synergistic effects with conventional therapies. Its antioxidants and nutrients reduce the side effects of chemotherapy drugs, while cancer-suppressing components may boost their effect [30, 31, 32, 33].
Health Benefits of Rehmannia
1) Enhancing Mood & Stress Resilience
In a study of 20 people with depression, a Rehmannia-containing combination of herbs improved mood after four weeks. Six people experienced significant improvements, while six had some improvement. It’s difficult to say whether Rehmannia was the herb responsible for these benefits, and since no control was included, any response could just be a placebo effect .
In another study, mice were subjected to bouts of unpredictable, chronic mild stress – a model that loosely correlates with human depression. Rehmannia improved the decreased antioxidant capacity in mice stressed in this way. It boosted key antioxidant enzymes, glutathione, and SOD .
Additionally, a sugar extract from Rehmannia decreased anxiety in rats. Complex sugars from its root could block proteins linked to anxiety in the hippocampus. This brain region is important for emotional balance, stress resilience, and memory storage. Its abnormalities are linked to both anxiety and depression [16, 36].
2) May Protect the Brain
Rats with dementia given a Rehmannia extract performed better on memory and learning tests. Catalpol also protected brain cells in dishes and helped them survive the effects of bacterial toxins. Its brain-protective effects are probably closely linked to its ability to lower the stress response, neutralize free radicals, and affect important brain regions like the hippocampus [17, 37].
3) May Fight Fatigue & Improve Endurance
Rehmannia is often described as an invigorator or a tonic – essentially, a substance to wake you up and make you feel more energized. Anecdotal evidence for this effect is abundant, but the actual scientific studies are scarce.
Tonics like Rehmannia may help the body adapt to stress and increased physical demands. However, additional studies on these effects are lacking [39+].
4) May Help Diabetes
Rehmannia, alone or in combination with other herbs, holds promise for diabetes. In one study, its components lowered blood sugar and improved kidney function in diabetic rats. Aside from its effects on glucose control, it may reduce diabetic complications. In one study, it decreased the size of diabetic foot ulcers in rats [21, 6+, 21, 40, 28+].
In an analysis of 18 clinical studies including over 1,200 people with diabetes, adding Rehmannia-containing Liuwei Dihuang Pills to typical western medicine regimes improved kidney function. However, the quality of the analyzed studies wasn’t great .
5) Improving Anemia
Aplastic anemia is a rare disease in which the body stops making enough blood cells due to bone marrow damage. In a clinical study of 34 people with this disease, Rehmannia extract added to standard treatment sped up symptom remission better than standard treatment alone .
A combination of traditional medicines, including Rehmannia, had promising effects in another trial of 64 people with the same type of anemia. An integrative medicine approach could protect the bone marrow and red blood cells and reduce inflammation. As a result, 12 people were “basically cured” .
6) May Reduce Inflammation
In rats, an extract of Rehmannia and another herb decreased inflammation after liver damage and reduced scarring. Sugars from this plant also lowered liver inflammation in mice. These benefits were confirmed in mice and rats with diabetes. What’s more, Rehmannia decreased the inflammatory activity of mouse immune cells [44, 45, 14, 46, 24, 47].
Contrastingly, in one study of rats with arthritis, Rehmannia extract didn’t have any effect on inflammation. However, this extract did have some beneficial effects, like improving circulation .
7) Preventing Bone Loss
Rehmannia, in combination with other herbs, may prevent bone loss. An analysis of over 100 studies including Rehmannia found that herbal formulations were generally effective, although many of the studies had limitations [48+].
8) Kidney Health
In a study of 72 people with nephrotic syndrome (a type of kidney failure), some people were given Liuwei Dihuang Pills as an add-on to standard treatment. The herbal pills improved kidney function better than the standard treatment alone .
In a similar study of 64 people with lupus nephritis – a kind of kidney inflammation – those who were given Liuwei Dihuang Pills in addition to standard treatment also had improved kidney function .
In a larger study of 479 people with chronic kidney inflammation, Rehmannia in addition to the standard care improved symptoms of kidney damage and inflammation .
This herb’s beneficial effects on kidney health were confirmed in several animal studies [28+].
Notably, the benefits vary depending on how the roots were prepared: dry, raw, and steamed Rehmannia roots each had different effects on the kidneys of rabbits. Only dry and steamed Rehmannia reduce renin, which would be beneficial for people with high blood pressure caused by kidney disease (renal hypertension). Raw Rehmannia, on the other hand, increased renin [29+].
9) May Help With Allergies and Asthma
Despite a long history of use as a remedy for allergies and asthma, there are few studies directly examining how Rehmannia affects these conditions. In rats with allergies, its extracts decreased inflammatory symptoms. Similarly, an extract of this herb lowered inflammation and skin lesions in mice with eczema [54, 55, 56].
In a study of 60 people with throat cancer, those given a Rehmannia extract had better short-term response rates and fewer radiation-related side-effects .
Heart Rate Variability
Heart rate variability measures how much your heart rate fluctuates. A higher heart rate variability is desirable. It’s linked to good health, better emotional control, and indicates a dominance of the rest-and-digest nervous system. A lower heart rate variability indicates a dominance of the fight-or-flight nervous system, which is associated with stress, anxiety, and inflammation [60, 61, 62].
Since Rehmannia may lower anxiety and depression, one would assume that it activates the rest-and-digest response. However, two studies of 160 healthy people showed mixed effects. Given as pharmacopuncture–herbal medicine injected into acupuncture points–Rehmannia activated both the fight-or-flight and rest-and-digest response, with the normal range [63, 64].
While these findings may sound confusing, it’s possible that this invigorating herb has some balancing action on the nervous system. What exactly it does, though, needs to be researched in more detail.
Rehmannia for Pets
There are a lot of anecdotal reports and pseudo-scientific claims about using Rehmannia to treat diseases in veterinary medicine, especially kidney failure. It is used in dogs, cats, and even horses. However, there isn’t actually much hard scientific evidence to back this up.
Some veterinarians use Rehmannia as part of an integrative approach to treatment regardless, but scientific studies in animals other than rats and mice are virtually nonexistent. The existing clinical trials support the effects on kidney health, but it’s unknown exactly how its active components are processed by animals.
There are a few scattered reports of individual animals with seizures or other brain problems improving from traditional techniques – often Rehmannia in combination with other herbs and acupuncture. However, these reports are scarce and Rehmannia was only one of the treatment modalities. It’s hard to say what, if any, effect it had [65, 66].
The most commonly noted side effects of Rehmannia are stomach problems like tenderness, nausea, and diarrhea. However, many published studies did not report what, if any, side effects were experienced [28+, 34+].
Rehmannia pharmacopuncture (herbal injections) partially activates the fight-or-flight nervous system. If you suffer from stress and anxiety, carefully watch your response to Rehmannia. In the traditional sense, this herb is considered to be an invigorating tonic and it’s unknown if it can trigger a negative reaction in people with high anxiety.
There isn’t currently enough evidence to say whether Rehmannia is safe in particular groups, like pregnant or breastfeeding women and children. The herb’s proponents tout its long history of safe use, but pregnant or breastfeeding women and children should avoid it until more clinical data are available [1+, 67].
Because Rehmannia can affect blood sugar, people with diabetes should exercise caution in taking Rehmannia, especially if they’re already on medication. It’s always best to ask your healthcare provider what the exact risks are for your specific situation before supplementing [28+].
Limitations and Caveats
Despite its long history in traditional medicine, there are relatively few studies on the efficacy of Rehmannia. Therefore, it’s important not to give too much weight to the result of any one study.
Most studies available are based on animal models. Mice and rats don’t always respond to diseases or treatments in the same way people do, so it’s unknown if the benefits will hold true in humans.
Of the available studies on humans, many of them are of relatively poor quality. Some lacked control groups, and many did not provide sufficient details of their methods, such as the exact herbal formulations used [28+].
Almost every study was performed on people with diseases or animals with modeled diseases. It’s important not to assume that this herb would benefit healthy people just because it might work for those living with a specific disease.
Finally, because herbal remedies are not especially well-regulated, and because the composition and effect of Rehmannia can vary depending on how it is prepared and what, if any, other ingredients it’s used with, it’s unwise to assume that any two products labeled or containing Rehmannia will necessarily have the same effects.
Whether and how Rehmannia interacts with other drugs has not been thoroughly investigated.
However, Rehmannia and/or other traditional herbs have been used in combination with standard of care Western medicine, often with beneficial results.
These findings suggest that Rehmannia can be safely added to Western medical treatment regimes, though such decisions should always be made in consultation with a healthcare professional. [53, 52, 51, 34].
Rehmannia roots can be prepared in a variety of ways, including raw, baked, and steamed. The roots can also be brewed into a tea. Rehmannia extracts can also be prepared, and Rehmannia can be taken in pills like Liuwei Dihuang Pills [68, 6, 3, 7].
However, Rehmannia supplements are not standardized, so the “strength” of different formulations can vary greatly.
One of the problems with the studies on Rehmannia in humans is a lack of dosage information. Some studies used Liuwei Dihuang Pills but didn’t report the amount of each component in the pills. This makes it difficult to determine what an optimal dose should be [28+].
Among available studies, dosages range from as little as 3 mg of Rehmannia to as much as 400 mg. However, many of these studies also included other herbs, so the dosage of Rehmannia was lower than it might have been if this herb was used alone [34+, 28+, 53].
Generally, users reported high satisfaction. They claim that taking Rehmannia helped with various health issues, like kidney problems or diabetes symptoms.
Anecdotal reports also strongly support the tonic effect of Rehmannia, with users saying it helps them feel energized and gives a sense of “well-being.”
Some reviews are less encouraging, reporting the development of infections and stomach discomfort.
Rehmannia is a herb used in Chinese traditional medicine, classified as an invigorating tonic for states of yin deficiency. Research on its benefits is sparse, although it shows promise for combating stress, low mood, fatigue, and kidney diseases. It may also help lower blood sugar and improve anemia. Added to conventional therapies, this herb may act in synergy and reduce the negative effects of some drugs, including those for treating cancer.
The roots of Rehmannia are used to prepare combination herbal products, usually of up to 6 ingredients. Although generally considered safe, supplements from this herb may cause stomach discomfort.