Although used in traditional medicine over centuries to treat digestive disorders and pain, it has no clinical evidence of safety or efficacy and may be toxic if ingested, and so has been commercially banned in the United States.

[4] The leaves are erect yellowish-brown, radical, with pink sheathing at their bases, sword-shaped, flat and narrow, tapering into a long, acute point, and have parallel veins.

The sweet flag can be distinguished from iris and other similar plants by the crimped edges of the leaves, the fragrant odor it emits when crushed, and the presence of a spadix.

Each flower contains six petals and stamens enclosed in a perianth with six divisions, surrounding a three-celled, oblong ovary with a sessile stigma.

The branched, cylindrical, knobby rhizome is the thickness of a human finger and has numerous coarse fibrous roots below it.

[7] Sweet flag grows in India, Nepal, central Asia, southern Russia and Siberia, Europe and North America.

[3][4] The generic name is the Latin word acorus, which is derived from the Greek άχόρου (áchórou) of Dioscorides (note different versions of the text have different spellings).

[9][10][11] The specific name calamus is derived from Greek κάλαμος (kálamos, meaning "reed"), cognate to Latin culmus ("stalk") and Old English healm ("straw"), Arabic قَلَم‎‎ (qálam, "pen"), in turn from Proto-Indo European *kole-mo- (thought to mean "grass" or "reed").

[13] Initially, Europeans confused the identity and medicinal uses of the Acorus calamus of the Romans and Greeks with their native Iris pseudacorus.

Thus the Herbarius zu Teutsch, published at Mainz in 1485, describes and includes a woodcut of this iris under the name Acorus.

This German book is one of three possible sources for the same error in the French Le Grant Herbier, written in 1486, 1488, 1498 or 1508, which was also published in an English translation as the Grete Herball by Peter Treveris in 1526; all of these contain the false identification printed in the Herbarius zu Teutsch.

The triploid form is the most common and is thought to have arisen relatively recently in the Himalayan region through hybridisation of the diploid with the tetraploid.

The comprehensive taxonomic analysis in Plants of the World Online from 2023 considers all three forms to be distinct varieties of a single species.

[4] Major components of the oil are beta-asarone (as much as 75%), methyl isoeugenol (as much as 40%) and alpha-asarone, saponins, lectins, sesquiterpenoids, lignans, and steroids.

[4][32] Although limits on consumption in food or alcoholic beverages (115 micrograms per day) were recommended in a 2001 ruling by the European Commission, the degree of safe exposure remained undefined.

[31] Allegedly, the plant is psychoactive (hallucinogenic), but for example all experiments with American calamus have been completely unsuccessful, even those involving very high dosages (up to 300 g of rhizomes).

It has been used medicinally for a wide variety of ailments, such as gastrointestinal diseases and treating pain, and its aroma makes calamus essential oil valued in the perfume industry.

[44] However, asarone's toxicity and carcinogenicity in mammals (including humans) means that it may be difficult to develop any practical medications or insecticides based on it.