Contents
Sweet flag (Acorus calamus) is a marsh plant whose aromatic rhizome has been used for centuries in Ayurvedic, Chinese, and European folk medicine — mostly to settle the stomach, calm the nerves, and ease aches. That long history is real. What’s missing is the part most articles skip: there are almost no good human studies behind those uses, and the plant’s rhizome oil contains β-asarone, a compound that regulators treat as a probable carcinogen. The U.S. Food and Drug Administration has banned calamus and its oil from food since 1968 [FDA, 21 CFR 189.110].
So here’s the honest version of sweet flag’s “health benefits.” The traditional reputation is interesting and worth understanding. The safety picture means you should not be drinking calamus tea or taking it as a supplement, and any use is best kept external and cautious. This article walks through what the plant is, what it’s traditionally been used for, how strong (or weak) the evidence actually is, and the safety facts that matter most.
What sweet flag is
Sweet flag is a tall, reed-like perennial that grows along the edges of marshes, ponds, and slow rivers across Asia, Europe, and North America. It goes by several names — calamus, sweet sedge, sweet rush, myrtle flag, and bacha or vacha in Ayurvedic texts. The part used medicinally is the rhizome, the thick underground stem, which is dried and powdered or distilled into an essential oil sometimes called oleum calami.
Botanically it sits in its own small family, Acoraceae (older references place it in the arum family, Araceae) [Sharma et al., J Clin Med, 2020]. Chemically, the rhizome is dominated by phenylpropanoids — chiefly the asarones and eugenol — plus a large mix of sesquiterpenes. More than 140 compounds have been isolated from it, but the asarones are the ones that drive both its traditional effects and its safety problems.
One detail matters more than any benefit claim: not all sweet flag is chemically the same. The amount of β-asarone varies enormously by plant type. The North American and European varieties contain little to none, while some Asian varieties can be up to 96% β-asarone by content of the oil [WebMD / Therapeutic Research Center, 2026]. Because a dried root or a bottle of oil rarely tells you which variety it came from, you usually can’t know how much of the problem compound you’re getting.
The safety issue, up front
β-asarone has been reported as genotoxic and carcinogenic in rodents, with tumors seen in the liver and small intestine in animal studies [Koh et al., Front Pharmacol, 2015]. That animal evidence is exactly why the FDA prohibits calamus, oil of calamus, and calamus extract as food additives — food containing them is legally considered adulterated in the United States [FDA, 21 CFR 189.110]. Consumer health references summarize it plainly: taken by mouth, calamus is likely unsafe [WebMD / Therapeutic Research Center, 2026].
Europe hasn’t banned the plant outright but has set a cautious ceiling. A temporary exposure limit of roughly 2 micrograms of β-asarone per kilogram of body weight per day has been applied to herbal products pending a full risk assessment — and when researchers actually tested herbal products on the market, some contained 4 to 25 times more β-asarone than that recommended level [Koh et al., Front Pharmacol, 2015]. The same work documented a case where a calamus-containing product with high β-asarone was suspected in liver toxicity in a three-month-old infant, and showed that asarones damaged human liver cells in the lab through oxidative stress.
The takeaway isn’t panic — it’s proportion. A single accidental exposure is not the concern regulators have. Repeated internal use over weeks or months is. That’s the pattern to avoid.
Traditional uses — and how strong the evidence really is
Sweet flag shows up in traditional medicine across dozens of countries, most consistently for digestion, calm, and pain [Sharma et al., J Clin Med, 2020]. Understanding those uses is reasonable. Just keep the evidence grade in mind: nearly all of it is traditional practice and animal or test-tube research, not human clinical trials. As WebMD’s herbal reference puts it, there is “no good scientific evidence” to support these uses in people [WebMD / Therapeutic Research Center, 2026].
Digestion and appetite
This is sweet flag’s oldest and most widespread reputation. Across India, Europe, and East Asia the dried rhizome was used as a bitter tonic to stimulate appetite, ease bloating and gas (a “carminative”), and settle an unsettled stomach [Sharma et al., J Clin Med, 2020]. There’s some laboratory and animal support for a mechanism here — extracts have shown antispasmodic activity on gut tissue — but that’s a long way from a demonstrated benefit in people, and it doesn’t override the safety problem with swallowing the plant.
Evidence grade: traditional use, with limited preclinical support; no reliable human trials.
Calm, sleep, and the nervous system
Sweet flag was traditionally treated as a mild sedative and nerve tonic — in Ayurveda it’s classed among the medhya (mind-supporting) herbs, and European folk practice added its decoction to warm baths to relax muscles and encourage sleep [Sharma et al., J Clin Med, 2020]. Animal studies have found various effects on the central nervous system, which is biologically interesting but not the same as showing it helps humans relax or sleep. If sleep is what you’re after, the better-studied options are covered in our guide to natural approaches for insomnia.
Evidence grade: traditional use plus early animal research; no human evidence.
Aches, joints, and skin
External use is where sweet flag’s traditional role is gentlest and its risk lowest. A decoction of the rhizome was added to bathwater to soothe rheumatic aches and calm itchy, irritated skin [Sharma et al., J Clin Med, 2020]. Applied to the skin rather than swallowed, the body’s exposure to β-asarone is far lower — though “lower” is not the same as “studied,” and even topical safety data is thin [WebMD / Therapeutic Research Center, 2026]. If you’re dealing with inflammatory joint pain, an anti-inflammatory eating pattern has more behind it than a herbal bath; see our overview of a rheumatoid arthritis diet.
Evidence grade: traditional use; minimal formal evidence.
Memory, infection, and the rest
You’ll see sweet flag promoted for memory, mood, infection, and more. Most of these trace to Ayurvedic tradition and to laboratory studies — for example, extracts have shown antimicrobial and neuroprotective activity in the lab and in animals [Sharma et al., J Clin Med, 2020]. Lab and animal findings are a starting point for research, not a reason to take a banned substance.
Evidence grade: preclinical or traditional only; insufficient for human recommendations.
Realistic expectations
If you strip away the marketing, sweet flag is a plant with a rich traditional story and a genuinely unresolved safety profile. It has not been shown in humans to cure, prevent, or treat any disease, and the compound that gives its oil much of its character is the same one that keeps it out of the food supply. Treat it as an object of interest and tradition — not as a supplement to add to your routine.
If you’re drawn to it for digestion, calm, or joint comfort, the more sensible path is to look at approaches with real human evidence behind them, such as the herbs and foods traditionally used for stomach issues or foods that support the nervous system, and to talk with a clinician before trying any herbal product.
Side effects, interactions, and who should avoid it
Because internal use isn’t advised, the most important safety facts are about what happens if someone takes it anyway — and about who is most vulnerable.
Reported side effects. Beyond the long-term cancer concern from β-asarone, taking calamus by mouth can cause nausea and vomiting, and it may lower blood pressure and slow heart rate [WebMD / Therapeutic Research Center, 2026].
Medication interactions. Calamus can interact with several drug classes. It may change how the liver processes medications broken down by the CYP2D6 and CYP3A4 enzymes, potentially altering their levels; it may add to the effects of sedatives and other central-nervous-system depressants, causing excessive drowsiness; it may interact with MAOI antidepressants; it can affect anticholinergic and cholinergic drugs; it may add to blood-pressure-lowering medications; and it can work against antacids, H2-blockers, and proton-pump inhibitors by increasing stomach acid [WebMD / Therapeutic Research Center, 2026].
Surgery. Because it affects the central nervous system, calamus could deepen the sedation from anesthesia. Stop using it at least two weeks before scheduled surgery [WebMD / Therapeutic Research Center, 2026].
Who should avoid it entirely:
- Anyone who is pregnant or breastfeeding. Calamus is rated likely unsafe by mouth during pregnancy and nursing; avoid it [WebMD / Therapeutic Research Center, 2026].
- Children, given the reported infant liver-toxicity case linked to a high-β-asarone product [Koh et al., Front Pharmacol, 2015].
- People with heart conditions, since large amounts may worsen some heart problems [WebMD / Therapeutic Research Center, 2026].
- People with liver disease, given the documented hepatotoxic potential of asarones [Koh et al., Front Pharmacol, 2015].
- Anyone taking the medications listed above, or scheduled for surgery.
When to talk to a healthcare professional
Reach out to a clinician before using any calamus product, especially if you take prescription medication, are pregnant or nursing, or have a liver or heart condition. Seek prompt medical care if, after using sweet flag in any form, you develop yellowing of the skin or eyes, dark urine, persistent nausea or vomiting, severe abdominal pain, unusual drowsiness or confusion, or a very slow or irregular heartbeat — these can signal liver stress or nervous-system or cardiac effects and should be evaluated the same day, or through emergency services if severe.
| Health Disclaimer This article is for general educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Sweet flag (calamus) is not approved for use in food in the United States, and taking it internally is considered likely unsafe. Nothing here should be read as a recommendation to consume it. Always speak with a qualified healthcare professional before using any herbal product — and especially if you are pregnant or breastfeeding, give it to a child, take prescription medication, have a liver or heart condition, or are scheduled for surgery. |
Frequently Asked Questions
Is sweet flag safe to consume?
For internal use, the honest answer is no. The FDA bans calamus, its oil, and its extract from food because of the cancer risk from β-asarone, and consumer health references rate it likely unsafe taken by mouth [FDA, 21 CFR 189.110], [WebMD / Therapeutic Research Center, 2026]. External use carries lower exposure but hasn’t been well studied for safety either.
Does sweet flag actually help digestion?
It has a centuries-long reputation as a digestive bitter and carminative, and there’s some laboratory support for an antispasmodic effect, but no reliable human trials confirm a benefit — and that traditional use involves swallowing it, which isn’t advised [Sharma et al., J Clin Med, 2020], [WebMD / Therapeutic Research Center, 2026].
Are some types of sweet flag safer than others?
Chemically, yes. North American and European varieties contain little to no β-asarone, while some Asian varieties can be up to 96% β-asarone in the oil. The practical problem is that most products don’t identify their variety, so you can’t rely on getting a low-asarone type [WebMD / Therapeutic Research Center, 2026].
Can I use sweet flag while pregnant or breastfeeding?
No. It’s rated likely unsafe by mouth during pregnancy and breastfeeding and should be avoided [WebMD / Therapeutic Research Center, 2026].
Why is it still sold if the FDA banned it?
The 1968 order bans calamus as a food additive; it doesn’t police every dried root or essential oil sold for other stated purposes. Availability isn’t a safety endorsement [FDA, 21 CFR 189.110].
References
- U.S. Food and Drug Administration. “21 CFR 189.110 — Calamus and its derivatives.” Electronic Code of Federal Regulations (current as of 2026). View source
- Therapeutic Research Center / WebMD. “Calamus: Uses, Side Effects, and More.” WebMD Vitamins & Supplements (© 1995–2026). View source
- Sharma V, Sharma R, Gautam DS, Kuca K, Nepovimova E, Martins N. “Role of Vacha (Acorus calamus Linn.) in Neurological and Metabolic Disorders.” Journal of Clinical Medicine, 2020;9(4):1176. doi:10.3390/jcm9041176 (PMID 32325895). View source
- Koh HL, et al. “Hepatotoxic potential of asarones: in vitro evaluation of hepatotoxicity and quantitative determination in herbal products.” Frontiers in Pharmacology, 2015;6:25. doi:10.3389/fphar.2015.00025. View source
