Cinnamon Supplements: Blood Sugar Evidence, Species and Safety

What is cinnamon?

Cinnamon is the dried inner bark of several trees from the same family. Cassia is the common, cheaper kind. Ceylon, or “true cinnamon,” is less common. Cassia contains coumarin, a natural compound that can harm the liver at high intakes while Ceylon has only traces of it. Between cassia and Ceylon, Ceylon carries less coumarin. For blood sugar, no trial has shown either kind is better; most trials used cassia.

People take cinnamon pills for blood sugar, cholesterol, and weight.

There is no officially recommended daily amount. Capsules usually hold 500 mg to 1.2 g of bark per serving; 1 g equals 1,000 mg.

Older medicinal uses and today's blood-sugar claims

NCCIH^[1] records medicinal use of cinnamon in China, India and Persia for complaints including pain and cough. Ancient trade accounts and Egyptian records also mention cinnamon or cassia. ^[2]

Today's studies examine the effect cinnamon has on blood sugar, blood fats and, in smaller groups, polycystic ovary syndrome (PCOS).

What people take cinnamon for

Cinnamon pills are optional supplements. In people with type 2 diabetes, a cinnamon supplement lowered fasting blood sugar a little on average, with results that varied widely between trials.

When to ask a doctor before taking cinnamon pills

• You take diabetes medicine. Cinnamon may lower blood sugar and add to the medicine’s effect.
• You have liver disease or take drugs that can affect the liver. Do not take cassia pills, since its coumarin can strain the liver; ask your doctor before taking Ceylon.
• You are pregnant. Skip cinnamon pills of either kind; the Pregnancy section explains the boundary between supplements and ordinary seasoning.

Amounts used in studies and the coumarin limit

There is no recognized recommended daily amount for cinnamon. The German Federal Institute for Risk Assessment^[3] gives a tolerable daily intake of 0.1 mg coumarin per kilogram of body weight: 6 mg for a 60 kg (132 lb) adult. Its monitoring data averaged about 3 mg coumarin per gram of cassia, so about 2 g reaches that intake before other sources are counted. Concentrations vary; the figure is a long-term exposure benchmark, not a threshold at which one serving causes injury.

No trial has shown that morning or evening use is better.

All forms at a glance

Ceylon and cassia compared

The German Federal Institute for Risk Assessment^[3] describes these visible differences, but says the powders are difficult for consumers to distinguish.

Ceylon and cassia supplements compared

Compare bark products by species and bark weight, converting milligrams when needed. For water extracts, compare the actual preparation rather than equating 500 mg extract with 500 mg bark. Water extraction can change coumarin content, but it does not prove that every finished extract contains none. Skip labels that do not name the species, labels that list several species with “and/or,” “natural metformin” claims, and daily gram amounts of cassia for months. ^{[4] [5]}

What to pay attention to on the label

Which number on the label is the amount?

Find the bark amount per serving—shown in grams or milligrams—and the species name. One product lists 1.2 g per two capsules; that equals 1,200 mg for the serving. Then look for Cinnamomum and a species. C. verum or C. zeylanicum is Ceylon. C. cassia, C. aromaticum, C. burmannii, or C. loureiroi is cassia. If no species is named, assume cassia. A 2013 US study found coumarin in every store cinnamon, cinnamon-flavored food, and cinnamon supplement it tested, most likely from Indonesian cassia (C. burmannii).

Misleading labels

Several species with “and/or”

One product lists 1.2 g of bark per two capsules from C. verum “and/or” aromaticum “and/or” burmannii. That means the capsules could be mostly cassia, and you cannot tell the coumarin content.

“True cinnamon” without a Latin name

One 500 mg product says “true cinnamon” and “Ceylon” but lists no Latin name. Look for C. verum or C. zeylanicum to identify Ceylon. Its lower coumarin content is a safety distinction; the glucose trials have not established that Ceylon is more effective than cassia.

Confusing servings and items per serving

Some manufacturers put 180 capsules on the front, and the back says 3 capsules per serving and 60 servings. The amount on the Supplement Facts panel is for the whole 3-capsule serving.

Common Myths about Cinnamon

Is cinnamon a natural metformin?

No. Metformin lowers HbA1c and has long-term trials showing fewer diabetes complications; cinnamon has neither consistently.

Is cinnamon good for the liver and kidneys?

Not shown, and cassia can harm the liver at high intakes because of coumarin.

Is all cinnamon the same?

No. Species changes the coumarin content enormously, and a 2018 paper by scientists linked to the US Pharmacopeia warned that trial results cannot be applied across species when papers do not name them.

Drawbacks and side effects

Reported side effects

Trials reported stomach upset and allergic reactions, but the evidence does not establish how common they are at a given dose. Topical cinnamon oil or powder can irritate skin or cause contact dermatitis; that route has different risks from eating cinnamon. ^[1]

When too much is dangerous

There is no official upper limit for cinnamon, only the coumarin limit above. Ceylon generally contains far less coumarin than cassia; long-term supplement amounts remain poorly studied. Cassia at 1 to 2 g or more a day can exceed the coumarin limit, which matters most over months.

Do not take cinnamon pills if you have liver disease without medical advice, do not plan gram amounts of cassia for months, and do not use cinnamon to replace prescribed diabetes medicine. If you already take cassia in gram amounts or develop symptoms that concern you, tell your clinician. A liver test can help investigate possible injury.

Do not try the “cinnamon challenge,” swallowing a spoonful of dry powder; NCCIH calls it unsafe.

Pregnancy

NCCIH advises against Ceylon cinnamon in supplement amounts during pregnancy. Cassia pills also add coumarin and have no established safe pregnancy dose. Skip cinnamon pills of any kind while pregnant; ordinary amounts used to season food shouldn't be a problem unless you have one of the conditions that warrant extra care.

The science behind cinnamon

The evidence shows a modest, inconsistent drop in fasting blood sugar, mostly no statistically clear HbA1c difference, and a real liver concern with cassia.

Blood sugar

A 2003 trial split 60 people with type 2 diabetes into six groups of 10: three took 1, 3, or 6 g of cassia and three took a placebo, for 40 days. Fasting blood sugar fell from their own starting levels on all cassia doses; that before-and-after comparison is weaker evidence than a direct comparison with placebo. In 2025, the journal issued an expression of concern about the study’s statistical methods. Its 3 g and 6 g cassia amounts also exceed the coumarin limit described above.

A 2012 Cochrane review summarized 10 trials in 577 people with diabetes, mostly using cassia at about 2 g a day on average for 4–16 weeks:

• It called the fasting blood sugar effect unclear.
• It did not find a statistically clear HbA1c difference.

A 2013 review of 10 trials in 543 people with type 2 diabetes used 120 mg to 6 g a day for 4–18 weeks:

• It found fasting blood sugar about 25 mg/dL lower.
• Results varied widely. The analysis counted the 2003 trial’s three doses as three comparisons; that trial now carries the journal’s expression of concern.
• HbA1c did not change significantly.

A 2019 review of 16 trials:

• It found fasting blood sugar about 10 mg/dL lower.
• It did not find a statistically clear HbA1c difference.

A 2024 review of 24 trials did find HbA1c lower. The reviews included different trials, and why they disagree is not settled.

Two water-extract studies add detail without settling the species or dose question. A 22-person prediabetes trial^[4] used 500 mg/day of Cinnulin PF for 12 weeks and reported lower fasting glucose and systolic blood pressure than placebo. A separate trial^[6] enrolled 173 people with elevated glucose, of whom 137 completed two months of 250 mg CinSulin twice daily or placebo; it reported favorable glucose, insulin and cholesterol measures.

Polycystic ovary syndrome

Small PCOS trials have tested outcomes beyond diabetes. In a six-month trial^[7], 45 women were randomized to 1.5 g/day cinnamon or placebo; menstrual cycles were more frequent in the cinnamon group, but only 17 completed the full study. A 12-week trial^[8] enrolled 66 women and reported improved insulin-resistance measures with 1.5 g/day cinnamon powder. Another 84-person trial^[9] reported favorable glucose, insulin and some lipid measures. These findings make PCOS worth discussing, while different preparations, short follow-up and small completed groups prevent a reliable treatment recommendation.

Cholesterol and blood pressure

The 2013 review:

• It found LDL, often called “bad” cholesterol, about 9 mg/dL lower.
• It found triglycerides, another type of blood fat, about 30 mg/dL lower, again with widely varying results.

A 2020 review of 9 trials with 641 people found blood pressure about 5/3 mmHg lower (the top and bottom numbers, in the standard blood pressure unit), but only in trials using 2 g or less for over 8 weeks in people with obesity.

Coumarin and the liver

Coumarin can injure the liver in susceptible people, which is why the European tolerable intake exists. Cassia generally contains much more coumarin than Ceylon; the intake calculation above uses the German agency’s monitoring average.

What is still open

No trial has shown that cinnamon prevents diabetes complications, and few trials named the species they used. Laboratory proposals about insulin receptors or antimicrobial action do not establish digestive or infection treatment effects in people.

Labs

No test measures cinnamon or coumarin exposure. If you have already taken cassia in gram amounts for months, or you develop possible liver symptoms, a clinician may use liver tests to investigate injury.

Before the test if you already supplement

If liver tests are ordered while you take a cinnamon extract, tell the clinician the species, dose and last dose. There is no established cinnamon-stop interval for these tests. Liver-test preparation may include fasting and clinician-directed medicine changes^[10]. If possible liver injury is the concern, seek assessment promptly; a planned supplement pause is not a reason to postpone testing.

The bottom line

Cinnamon may produce small changes in some blood-sugar or blood-fat measurements, but the findings are inconsistent and do not make it a replacement for diabetes treatment. The species matters for safety as well as for interpreting the research.

Cassia can supply substantial coumarin, while Ceylon generally supplies much less. We would not increase a cinnamon supplement intake simply to imitate a high-dose trial. Check the species, preparation and amount, when buying a supplement, but keep in mind that most label claims have weak scientific basis.

We do love cinnabons though.

Source notes

• National Center for Complementary and Integrative Health: cinnamon^[1]
• ^[4]
• ^[6]
• ^[7]
• ^[8]
• ^[11]
• ^[12]
• ^[13]
• ^[14]; ^[15]
• ^[16]
• ^[17]
• ^[18]
• ^[19]
• ^[20]
• ^[21]
• ^[22]
• ^[23]
• ^[24]
• ^[25]

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