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Photo of Rehmannia Root

Rehmannia Root

生地黄 · Shēng Dì Huáng

Cools a body running hot and refills lost fluids

Properties

CoolingCooling botanicalSweet, Bitter

What it does

Rehmannia root is for when your body runs hot and dry, with a parched mouth, restless nights, and skin that flares red. In TCM it cools the blood and refills the fluids that heat has burned off, so practitioners use it for rashes, nosebleeds, and low-grade fevers that linger. It's rich and juicy, which is exactly why it can bog down weak digestion. Steaming it makes a different herb.

Safety

  • Not for waterlogged, weak digestion with loose stools and a bloated abdomen. This root is heavy and cold.
  • Do not take it if you currently have diarrhea.
  • Reported side effects: diarrhea, abdominal pain, dizziness, fatigue, and heart palpitations.
  • Allergic reactions have been reported, including one anaphylactic reaction after a very high dose.
  • Only limited information exists on use during pregnancy or breastfeeding, so safety is not established.
  • AHPA safety class 2d: specific use restrictions rather than a blanket warning.
  • The restriction here is the diarrhea contraindication above.
  • Don't confuse it with prepared rehmannia, which is warming and blood-building where this one cools and moistens.
  • Swapping them gets the pattern backwards.

How to take it

Drink

Simmer 9–15g of the sliced dried root in 4 cups water for 30–40 minutes and drink strained. Use stainless steel or ceramic: classical sources are specific that this root should not touch iron.

Simmer 9g for a few days when a lingering low fever or a hot, itchy rash won't settle

Where it comes from

Rehmannia root appears in the Shén Nóng Běn Cǎo Jīng. It's the unprocessed form of the root, and its Chinese name reads 'unprepared earth yellow.' Steam it repeatedly and it becomes a warm blood tonic instead, prepared rehmannia, whose name reads 'cooked earth yellow'. Classical writers described the raw root as purple at the core, yellow in the middle, and black outside, mapping it onto three organs at once, and the practical read is that raw rehmannia cools while cooked rehmannia builds.