An herbaceous, moisture-loving perennial that grows between six and ten inches in height and bears greenish-yellow blossoms throughout summer, Houttuynia cordata is an herb of minor importance in traditional Chinese medicine. The plant is used as a folk medicine wherever it is found naturally, particularly to help heal lung abnormalities, earache, infectious disease, water retention, detoxification and general debility. Exploratory studies by Chinese scientists have indicated that extracts of the plant may possess antiviral, antibacterial, anti-herpetic, anti-obesity, and anti-leukemic properties. It may also be useful in the treatment of pneumonia or severe acute respiratory syndrome (SARS) coronavirus.
Much of the research conducted on Houttuynia cordata as of 2011 has neglected to distinguish between two different chemotypic varieties within the species, both of which likely possess dramatically different pharmacological properties. While the Southeast Asian chemotype has an essential oil profile that is quite similar to that of cilantro or coriander leaf, the Japanese chemotype possesses an unusual mix of citrus aromas that can best be compared to ginger, galangal or lemon myrtle. Some of the potentially therapeutically active compounds within the former include methyl nonyl ketone, limonene and myrcene as well as the potent antibacterial compound 3-keto-dodecanal, which is not found in the Japanese chemotype. The Japanese chemotype of Houttuynia cordata instead contains the related chemicals lauryl aldehyde, caprylic aldehyde and methyl nonyl ketone as well as a number of other biologically active pyridine alkaloids, flavonoids and flavonoid glycosides.
While 3-keto-dodecanol may be the most potent antibacterial agent in Houttuynia cordata, other compounds are likely responsible for its use in the treatment for symptoms of seasonal and chronic allergies as well as acute infectious respiratory illnesses. Preliminary studies suggest that the success of Houttuynia cordata preparations in controlling symptoms for these conditions is due to the plant's anti-inflammatory properties. While the compound or compounds responsible for Houttuynia cordata's anti-inflammatory properties have not been conclusively identified, whole extracts of the plant have demonstrated selective cyclooxygenase-2 (COX-2) inhibiting activity similar to that of prescription non-steroidal anti-inflammatory drugs. It is possible that the flavonoid glycosides quercetin and isoquercetin may be the source of this activity.
Despite its use in the treatment of allergies, Houttuynia cordata may itself be the cause of serious allergic reactions. There have been several reports of potentially fatal anaphylactic allergic reactions in patients using preparations of the plant. While rare, it is important to advise patients of the symptoms of an anaphylactic reaction if they intend to use this plant.
Houttuynia cordata is also known as heartleaf due to its shape and fishwort due to the unusual odor it produces when its leaves are crushed. The plant is most commonly cultivated for its use as a leaf vegetable or garnish in Vietnamese cuisine and as a root vegetable in south China. Due to its invasive nature, this herb should not be cultivated throughout many regions of the United States, Europe and Australia, as it can proliferate rapidly and displace native plant species.