Sprouting from the edges of lakes, ponds, and streams in muddy — and often stinky — areas, sweet flag (Acorus calamus) is quite an unusual plant. It's not just the fact that something that grows in such "yucky" places actually smells so good it's used in perfume, but also that it's been used as a medicine since... well, forever? Mentioned in the Bible (as one of the ingredients in an anointing oil), sweet flag originates from Asia and has been used in numerous traditional medicine disciplines — Ayurveda, Unani, Siddha, and Chinese medicine, among others. 
The traditional uses of the leaves and rhizomes (rootstocks) of Acorus calamus include the treatment of [1, 2]:
- Appetite loss
- Chest pain
- Colic in infants
- Digestive disorders — including flatulence, cramps, indigestion
- Vascular disorders
- Depression and other mental health concerns
Sounds like quite the wonder drug, no? That's what my friend thought, too. Acorus calamus grows in my "wider backyard" (I live on a nature reserve), you see, and we were out for a walk with her dog not long ago. The canine, who happens to have severe gastrointestinal issues, found its way to some sweet flag roots and started eating them. "What's that?", she asked, and I told her. A few Google searches later, mainly landing on articles like the one quoted above, she thought she'd found a miracle cure for just about anything, and added that her dog "knows what it needs".
The truth is more complex. We all know that the ancients did some pretty wacky things in their quest to cure people, including things that we now know to be quite dangerous but that contemporary fans of alternative medicine nonetheless hold up as wonderful. Does sweet flag's use as a medicinal herb hold up to modern science?
What Are The Pharmacological Properties Of Sweet Flag?
There really are a lot. You'd be surprised.
A 2013 review of studies conducted into the medicinal benefits of sweet flat (Acorus calamus) found that :
- The ethanolic (alcoholic) extract of sweet flag's rhizomes may act as an anti-ulcer medicine, as shown in a rat study.
- Acorus calamus, in the form of essential oil and the alcoholic extract of its rhizomes, can act as an analgesic (pain reliever).
- The rhizome extract has anti-inflammatory properties.
- Several gram-negative bacteria, including staphylococcus aureus, Escherichia coli and shigella flexneri, really don't like encountering sweet flag essential oil in a petri dish — yup, it indeed possesses natural antibiotic qualities!
- Sweet flag rhizome extract also has anti-epileptic properties.
Another review showed that Acorus calamus' leaves and rhizomes have antifungal and anti-yeast properties, that the plant may benefit diabetic patients, and that it indeed has some cancer-fighting abilities.  Yet other studies have found that Acorus calamus helps cure diarrhea, has a natural diuretic effect, and acts as a bronchodilator.  In addition, research suggests that beta-asarone, the active component in sweet flag, really does improve cognitive function . That's at least 10 uses that I can count; sweet flag does seem like a rather potent medicine!
Should You Use Sweet Flag?
The studies conducted, mostly by proponents of Ayurvedic medicine and many of them during the second half of the twentieth century, deserve further investigation — sweet flag seems to be a plant with much potential, and one from which new medicines could perhaps be synthesized in the future.
The very same active component that gives sweet flag its numerous beneficial effects, beta-asarone, is apparently carcinogenic [7, 8], and chewing sweet flag rootstock can induce hallucinations . Sweet flag has been deemed so dangerous that the Food and Drug Administration has banned its use in the United States .
The bottom line? Depending on where you live, you may be able to buy sweet flag extract or essential oil over the counter, and you may even have it growing somewhere near you. Before you find your particular ailment on the list of things Acorus calamus is apparently able to cure, however, remember that it may come with perhaps the most serious side effect of them all — cancer. Before you see sweet flag as a cure-all, if you live in a country where you have ready access to medicines that have gone through a rigorous scientific testing process, perhaps consider a medicine proven to be safe to treat your illness instead.