IngredientsHydrilla (waterthyme) is a genus of aquatic plants, usually treated as containing just one species — Hydrilla verticillata, though some botanists divide it into several species. The full accepted botanical name, as catalogued in the Royal Botanic Gardens at Kew's Plants of the World Online database, is Hydrilla verticillata (L.f.) Royle. The genus name derives from the Greek ύδωρ (hydro), meaning water, referring to its aquatic habitat, while the species epithet verticillata refers to the whorled arrangement of its leaves. Linnaeus himself originally named it Serpicula verticillata, and over the centuries it has borne numerous synonyms including Hottonia serrata, Hydrilla angustifolia, Hydrilla dentata, Leptanthes verticillatus, Vallisneria verticillata, and Udora verticillata. Claude Richard — likely Louis Claude Marie Richard (1754–1821) — established the genus name Hydrilla; as it was a monotypic genus, Linnaeus's species epithet verticillata was retained, resulting in the current combination.
The plant belongs to the family Hydrocharitaceae. Common names include waterthyme, water thyme, and hydrilla. In the dietary supplement trade it is almost universally sold under its Latin binomial or simply as "Hydrilla."
The plant is native to the cool and warm waters of the Old World in Asia, Africa, and Australia, with a sparse, scattered distribution; in Australia it occurs from the Northern Territory to Queensland and New South Wales. The native range, as catalogued by Kew Science, extends from Poland to Asia and from Australia to the West Pacific, as well as from Uganda to northern Zambia. Two biotypes exist with separate origins: the common dioecious type originates from the Indian subcontinent — historical reports specify Sri Lanka (Schmitz et al. 1991) while RAPD analysis points to India's southern mainland (Madeira et al. 1997) — while the monoecious type appears to originate from Korea (Madeira et al. 1997).
It is believed that Hydrilla is native to Asia and/or India and was first discovered in Florida in the 1960s; by 1988 it had spread to an estimated 20,000 hectares of water. Current distribution in the United States includes all southeastern states, Connecticut, Delaware, Maryland, Virginia, Alabama, Texas, Arizona, California, and Washington, and it has been listed as a Federal Noxious Weed, prohibited or restricted in eleven states.
The stems grow up to 2 metres long. The leaves are arranged in whorls of two to eight around the stem, each leaf 5–20 mm long and 0.7–2 mm broad, with serrations or small spines along the leaf margins; the leaf midrib is often reddish when fresh. It is monoecious (sometimes dioecious), with male and female flowers produced separately on a single plant; the flowers are small, with three sepals and three petals, the petals 3–5 mm long, transparent with red streaks. The plant primarily reproduces through turions (compact dormant buds) and tubers; turions are produced in the axils of the leaves and are condensed shoots 5 to 8 mm long with 12 to 15 internodes surrounded by alternating whorls of fleshy leaves. It can grow very rapidly — up to 2.5 cm per day — to reach the water surface.
Hydrilla verticillata is commercially available primarily in the following forms:
The plant has no official pharmacopoeial monograph in the European Pharmacopoeia, the USP, WHO monographs, ESCOP, or the German Commission E at the time of this writing.
Historical use of Hydrilla prior to it becoming classified as a "noxious" weed in Western countries is scant, limited to a few references regarding how it was named and certain localized uses. The ethnobotanical literature on this species as a human food or medicinal plant is far less extensive than for more extensively documented aquatic plants such as lotus (Nelumbo nucifera) or water cress.
Hydrilla verticillata is an aquatic plant that has garnered attention for its nutritional and medicinal properties; traditionally found in Asia, it has been utilized for centuries in various folk remedies and healing practices, and was historically valued by ancient cultures for its high concentration of vitamins, minerals, and antioxidants.
In the ancient Indian system of medicine known as Ayurveda, Hydrilla verticillata is recognized as a medicinal plant valued for its cleansing, restorative, and energizing properties. Hydrilla is somewhat mysterious in that not much is formally recorded about its origins other than mentions appearing in Indian Ayurvedic literature. It is important to note, however, that the depth and provenance of these Ayurvedic citations are difficult to verify in primary classical texts, and the claims circulating in the supplement trade should be treated cautiously. Plants have been associated with health, nutrition, and overall care of mankind since time immemorial, and Hydrilla verticillata (Linn.f.) Royle is credited with numerous biological activities.
Traditionally found in Asia, Hydrilla has been utilized for centuries in various folk remedies and healing practices. Historically, it was valued by ancient cultures for its high concentration of vitamins, minerals, and antioxidants. In traditional contexts, Hydrilla decoctions were reportedly used to support vitality, boost energy levels, and improve overall well-being. Its calcium and magnesium content was associated with bone-strengthening and nervous system support. Additionally, its chlorophyll and phytonutrient richness were believed to purify the blood and promote healthy digestion, and healers often recommended it as a tonic for immune support and recovery from fatigue or illness.
According to Kew Science's Plants of the World Online, Hydrilla verticillata is used as animal food, as a medicine, and for human food. In parts of Asia, the tender shoots of aquatic macrophytes including Hydrilla have been consumed as a leafy vegetable. However, systematic ethnographic documentation of specific preparation methods and populations for H. verticillata as a human food crop is limited in the peer-reviewed literature.
It should be noted that much of the "traditional use" narrative circulating in modern supplement marketing cannot be directly traced to verifiable primary historical sources such as classical Ayurvedic pharmacopoeial texts (Charaka Samhita, Sushruta Samhita, Ashtanga Hridayam) or Chinese materia medica such as the Bencao Gangmu. Sources acknowledge that Hydrilla is not normally recognized as part of the Traditional Chinese Medicine pharmacopeia. Claims about deep historical use should therefore be regarded as partly inferred rather than fully documented.
The plant is a rich source of variable nutrients and chemical constituents including saponins, vitamins, minerals, antioxidants, amino acids, and detoxifying agents. Phytochemical analysis has revealed the presence of alkaloids, phenols, flavonoids, saponins, and terpenoids.
Major chemical constituents identified by GC-MS analysis of the ethanolic extract include bicyclo(3.1.1)heptane,2,6,6-trimethyl (4.40%), 2-pentadecanone,6,10,14-trimethyl (4.77%), hexadecanoic acid ethyl ester (9.51%), phytol (70.29%), linoleic acid ethyl ester (2.08%), and 9,12,15-octadecatrienoic acid ethyl ester (8.96%). GC-MS studies have confirmed phytol and hexadecanoic acid ethyl ester as major components. A separate GC-MS analysis identified n-hexadecanoic acid (7.18%), hexadecanoic acid ethyl ester (13.29%), palmitic acid (12.09%), phytol (2.12%), linolenic acid ethyl ester (26.26%), and stigmasterol (11.39%) among other compounds.
One of the primary reasons Hydrilla verticillata has attracted interest as a dietary supplement is its reported nutritional density. Figures reported in product literature (attributed to laboratory analysis of dried powder at a 4.75 g serving size) indicate high concentrations of multiple micronutrients. Per approximately 4.75 g serving, reported values include calcium 624 mg (62.4% DV), iron 4.6 mg (25% DV), thiamin 7.2 mg (480% DV), niacin 13 mg (65% DV), vitamin B6 4.5 mg (225% DV), vitamin B12 475 mcg (7,750% DV), vitamin A 5,454 IU (109% DV), vitamin C 6.53 mg, riboflavin 0.26 mg, pantothenic acid 8.4 mg, magnesium 38.3 mg, chromium 7.4 mcg, copper 174 mcg, molybdenum 8.7 mcg, selenium 1.25 mcg, zinc 0.3 mg, boron 65 mcg, cobalt 174 mcg, silica 32.7 mg, GLA 3 mg, chlorophyll 16 mg, and polysaccharides 2 g.
Hydrilla verticillata hyper-accumulates calcium from the calcium-rich soils underlying rivers and lakes; the plant is 14% or more calcium by weight after drying. One level tablespoon of powder (approximately 4.75 grams) has been reported to deliver more than 700 mg of elemental calcium in a form complexed with proteins, carbohydrates, and other food factors in the plant.
Important caveat: These nutrient figures are derived from commercial product testing data circulated by manufacturers and have not been independently validated or reproduced in peer-reviewed publications that would meet scientific standards of analytical chemistry. They should be considered indicative rather than definitively established.
Hydrilla has been reported to contain approximately three times more beta-carotene than chlorella and is rich in most B-vitamins. Its green color is consistent with a significant chlorophyll content, which is characteristic of submerged aquatic macrophytes.
Research has shown Hydrilla contains a wide range of polysaccharides, which are widely recognized in the medical community for their immune- and general health-enhancing properties. The specific structural characterization and biological activity of the polysaccharide fraction of H. verticillata has not been as thoroughly characterized in the peer-reviewed literature as those of better-studied algae such as Spirulina or Chlorella.
Otteliones A and B, novel antitumor agents identified from a freshwater plant related to the Hydrocharitaceae family, were the subject of total synthesis and absolute configuration studies published in Organic Letters (Araki, Inoue, and Katoh, 2003). Hydrilla has been reported to contain otteliones A and B, which have been shown in studies to have potent anti-tumor effects. These compounds were originally characterized from Ottelia alismoides, a related Hydrocharitaceae member, and enantioselective total synthesis of otteliones A and B — described as novel and powerful antitumor agents from the freshwater plant Ottelia alismoides — was reviewed in Natural Product Communications (Katoh, 2013). The extent to which otteliones A and B are reliably present in commercial H. verticillata preparations has not been confirmed in independent peer-reviewed analyses.
One of the active compound classes in Hydrilla verticillata is steroids; research has aimed to isolate, identify, and determine their toxicity and antioxidant activity. Stigmasterol has been identified as a significant steroid component by GC-MS analysis. Steroid isolates from Hydrilla have been shown to possess antioxidant activity in laboratory investigations.
A critically important chemical property of H. verticillata with direct implications for supplement safety is its capacity to accumulate heavy metals from its aquatic environment. The shoots of Hydrilla verticillata have more ability in the translocation of toxic metal uptake than the roots; when exposed to high concentrations of lead solution for one week, Hydrilla showed 98% uptake of lead. Hydroponic experiments confirmed that, as an excellent heavy metal accumulator, H. verticillata showed an accumulation pattern of Ni > Cd > Pb within the experimental scope. In studies comparing submerged aquatic plants, H. verticillata was able to accumulate high amounts of arsenic (95.2%) and zinc (93.7%) from mine wastewater effluent, resulting in a decrease of these elements in the ambient water. Plant shoots showed a significant accumulation of arsenic, with a maximum of more than 700 μg g⁻¹ dry weight after exposure to 20 μM arsenate or arsenite for four days.
This extraordinary capacity for heavy metal hyperaccumulation has been studied extensively for phytoremediation purposes. The same property creates a direct safety concern for human consumption: plants harvested from polluted or inadequately monitored water bodies may carry unsafe loads of arsenic, lead, cadmium, nickel, or other toxic metals.
The overall state of the scientific literature on Hydrilla verticillata as a human dietary supplement is preliminary. Robust human clinical trials are currently lacking, and most health claims are based on in vitro or animal investigations rather than direct human evidence. The sections below review what has been studied, organized by area.
Evidence level: In vitro / laboratory (preliminary).
A study in the Journal of Chemical and Pharmaceutical Research evaluated the phytochemical constituents, antioxidant, and antimicrobial activity of ethanolic extract of Hydrilla verticillata. Phytochemical analysis revealed alkaloids, phenols, flavonoids, saponins, and terpenoids; GC-MS confirmed phytol and hexadecanoic acid ethyl ester as major components. The antioxidant activity was assessed by DPPH free radical scavenging assay, with free radical scavenging activity showing a maximum of 29.60% inhibition at 100 μg/mL.
Hydrilla verticillata contains active compounds with potential as antioxidants, antibacterials, anticancer agents, and antimicrobials; one of the active compound classes is steroids, which have been the subject of isolation and antioxidant characterization. A brine shrimp lethality test (BSLT) was used as a proxy toxicity screen: LC50 values of methanol extract, chloroform extract, and n-hexane extract of H. verticillata were 633,171 ppm, 624.55 ppm, and 16,762 ppm respectively.
In an animal (fish) feeding study, malondialdehyde levels dropped and antioxidant enzyme activity (SOD, CAT, and GPx) significantly increased in Hydrilla extract-fed groups, suggesting improved oxidative state. These findings are from an aquaculture model and cannot be directly extrapolated to humans.
No randomized controlled trials in humans have evaluated the antioxidant effects of Hydrilla supplementation.
Evidence level: In vitro / cell culture (preliminary).
Hydrilla verticillata is a perennial aquatic plant exhibiting nutritional as well as therapeutic properties; a study published in the Journal of Biomolecular Structure and Dynamics (2023) was carried out to evaluate anti-inflammatory and immunomodulatory activities along with in silico evaluation of potential selective COX-2 and TNF-α inhibitors from methanolic extract of H. verticillata. Potential therapeutic compounds were identified by high-resolution GC-MS analysis. The anti-inflammatory properties of the plant extract were investigated by inhibiting inducible nitric oxide (NO) synthase and reduced NO generation driven by LPS on stimulated RAW 264.7 macrophage cells.
The same research group conducted further molecular docking and molecular dynamics simulation studies to investigate the molecular mechanisms underlying the anti-inflammatory activity. These are computational and cell-line-based findings and have not been replicated in human trials.
Evidence level: In vitro (preliminary).
Studies on in vitro evaluation of antibacterial and antioxidant activity of H. verticillata tested methanolic and n-hexane extracts against five pathogenic bacteria — Enterococcus faecalis, Escherichia coli, Klebsiella pneumoniae, Shigella flexneri, and Vibrio cholerae — using agar well diffusion, with ciprofloxacin as a reference. The n-hexane extract showed the highest zone of inhibition against Enterococcus faecalis (20 ± 1.41 mm) and the least against Vibrio cholerae (12 ± 1.63 mm) at a concentration of 15 mg/mL.
The antimicrobial activity of the ethanolic extract exhibited greater inhibition zones against Gram-positive bacteria than Gram-negative bacteria; the extract had no activity against fungi. These findings provide evidence that Hydrilla verticillata is a potential source of secondary metabolites, natural antioxidants, and antimicrobial activity. All antimicrobial results are from in vitro agar diffusion assays; no animal or human studies of antimicrobial efficacy have been reported.
Evidence level: Preclinical (preliminary).
Hydrilla verticillata has been identified as potentially effective in different stages of arthritis and has been reported to give both preventive and therapeutic results against arthritis in preclinical investigations referenced in the phytochemical screening literature. The specific study designs, animal models, and effect sizes have not been reported in detail in the sources located, and no human clinical trials on this indication are available.
Evidence level: Animal study only (preliminary).
The aqueous extract of Hydrilla verticillata (AEHV) was tested for possible pharmacological activity in experimental animals. AEHV significantly potentiated the sleeping time of mice induced by standard hypnotics (pentobarbitone sodium, diazepam, and meprobamate) in a dose-dependent manner. AEHV also showed significant analgesic properties as evidenced by significant reduction in writhing and stretching induced in mice by 1.2% acetic acid solution, and it potentiated analgesia induced by morphine and pethidine in mice. These findings are limited to a rodent model and have no direct human clinical correlate established.
Evidence level: Controlled animal study (not human-applicable directly).
A study published in Veterinary Research Communications investigated the effects of dietary Hydrilla verticillata extract (HVE) on growth performance, physiological responses, and disease resistance in Labeo rohita (rohu) fingerlings subjected to Aeromonas hydrophila challenge. Fish were divided into 15 tanks (30 fish per tank) and given five different diets containing 0, 75, 150, 300, or 600 mg/kg HVE for 60 days. Growth was significantly (P < 0.05) boosted by dietary HVE, with 300 mg/kg showing the maximum weight gain and protein efficiency ratio; however, the higher dose (600 mg/kg) reduced growth performance. In HVE-fed groups, malondialdehyde levels dropped and antioxidant enzyme activity (SOD, CAT, and GPx) significantly increased, suggesting improved oxidative state. Elevated ALP, decreased AST and ALT activity, and decreased serum glucose and cortisol levels all indicated enhanced hepatic function and reduced stress. This fish model cannot be directly extrapolated to human use, but is notable as one of the few controlled studies using a quantified dosage of Hydrilla extract.
Evidence level: Nutritional/compositional analysis (no clinical trials).
Hydrilla contains high levels of calcium, vitamin B12, and iron, making it an especially valuable potential source of nutrition for vegetarians. The calcium, iron, and vitamin B12 content of Hydrilla are nutrients often dangerously low in pure vegetarian (vegan) diets. No published randomized clinical trial has measured whether Hydrilla supplementation effectively raises serum B12, ferritin, or bone mineral density in humans with deficiencies. The B12 values reported in product analyses are exceptionally high, but the bioavailability and chemical form (active cobalamin versus inactive analogues) of this B12 in H. verticillata has not been independently verified by peer-reviewed human studies.
Evidence level: Computational / preclinical (early stage only).
Molecular docking studies of selected phytosterols from Hydrilla verticillata on estrogen receptors have been conducted as candidates for anti-breast cancer investigation. The ottelione compounds identified in related Hydrocharitaceae species have attracted interest due to their antitumor properties in laboratory settings. All anticancer-related findings are currently at the in vitro or in silico stage; no clinical evidence exists.
Based on the available preclinical and nutritional literature, the following body systems and health areas have been associated with Hydrilla verticillata:
There is no established or regulatory-approved human dosage for Hydrilla verticillata. The following dosage information is drawn strictly from what appears in identified sources:
No peer-reviewed human clinical trials have established pharmacokinetically-based dosing recommendations, effective doses, or dose-response relationships in humans.
This is the most substantively documented safety concern for H. verticillata as a dietary supplement. Hydrilla verticillata is a submerged macrophyte widely distributed throughout the world with the potential to effectively remove heavy metals from water. As an excellent heavy metal accumulator, H. verticillata showed an accumulation pattern of Ni > Cd > Pb in controlled experiments. Plant shoots accumulated arsenic to a maximum of more than 700 μg g⁻¹ dry weight after exposure to 20 μM arsenate for just four days. In mine wastewater experiments, H. verticillata accumulated arsenic (95.2%) and zinc (93.7%) from the ambient water. Plants used for supplement production that are harvested from water bodies contaminated with industrial effluents, agricultural runoff, or other pollution sources therefore carry a real and verified risk of delivering concentrated heavy metals to consumers.
Vacuolar myelinopathy (VM), a fatal neurological disease initially discovered during a mysterious mass mortality of bald eagles in Arkansas, has been linked to a cyanobacterium (Aetokthonos hydrillicola) growing on the invasive plant Hydrilla verticillata in man-made water bodies. The cause of this wildlife disease eluded scientists for decades while continuing to spread throughout freshwater reservoirs in the southeastern United States. Recent studies demonstrated that VM is induced by consumption of the epiphytic cyanobacterial species A. hydrillicola growing primarily on H. verticillata. The causal agent has been identified as aetokthonotoxin, a pentabrominated biindole alkaloid produced by A. hydrillicola; its production is promoted by bromide availability in the environment.
Aetokthonotoxin has been reported to produce vacuolar myelinopathy, most often seen in coots and bald eagles that prey on affected waterfowl. The toxin is produced by cyanobacteria growing on exotic invasive Hydrilla verticillata in southern lakes and reservoirs in the United States. Turtles and tadpoles that fed on contaminated Hydrilla experienced similar neurologic damage, reproduced experimentally in turtles.
Aetokthonotoxin has been identified as the cause of vacuolar myelinopathy — a fatal neurological condition linked to deaths in wildlife including eagles, waterfowl, fish, and bobcats — and the potential for toxin transfer through the food chain raises emerging concerns for human health. Scientists at the Wadsworth Center have developed a novel molecular assay to evaluate the risks posed by the emerging toxic cyanobacterium Aetokthonos hydrillicola, which is capable of producing two potent toxins: aetokthonotoxin, a brominated neurotoxin, and aetokthonostatin, a cytotoxic dolastatin analog. Whether aetokthonotoxin occurs in commercially harvested Hydrilla supplement material has not been systematically evaluated in the published literature; however, the risk is not hypothetical given that the cyanobacterium specifically colonizes H. verticillata in U.S. water bodies.
Hydrilla verticillata hyperaccumulates bromide from the environment, potentially supplying the cyanobacterium with the biosynthesis precursor required for aetokthonotoxin production.
Aquatic plants in several families, including Hydrocharitaceae, have been documented to contain the enzyme thiaminase, which cleaves thiamine (vitamin B1) and can cause thiamine deficiency when consumed in large amounts over time. The patent literature on thiaminase notes its context in cancer research. No specific peer-reviewed clinical safety data regarding thiaminase content and activity in commercially prepared H. verticillata supplements, or its implications for human vitamin B1 status at supplement doses, has been located in the sources reviewed.
In the United States, Hydrilla verticillata as a dietary supplement ingredient has not been the subject of a Generally Recognized As Safe (GRAS) determination by the FDA, and it is classified as a Federal Noxious Weed in its aquatic form. It has been listed as a Federal Noxious Weed and is prohibited or restricted in eleven states. Harvesting and transport of the plant may be legally restricted in many U.S. jurisdictions. No European Food Safety Authority (EFSA) safety assessment or Novel Food authorization has been identified in the publicly available literature for this species used as a food ingredient.
No peer-reviewed clinical or pharmacokinetic studies specifically addressing drug interactions with H. verticillata preparations have been identified in the sources reviewed. Given the very high reported B12 content (if confirmed to be active cobalamin), interactions with medications affecting B12 metabolism (e.g., metformin, proton pump inhibitors) are theoretically possible but have not been studied. The high calcium content raises potential interactions with calcium channel blockers, bisphosphonates, and fluoroquinolone antibiotics, as is the case for any high-calcium supplement.
Given that the entire safety profile of any H. verticillata supplement is heavily dependent on the quality of the water body from which it is harvested, wildlife VM deaths occurred only in reservoirs with dense H. verticillata and A. hydrillicola populations, and the absence of standardized testing protocols for aetokthonotoxin and heavy metals in commercial Hydrilla supplement products is a significant unresolved concern in the literature.
The table below summarizes the overall evidence state for the main proposed applications of Hydrilla verticillata as a dietary supplement:
Robust human clinical trials are currently lacking, and most health claims are based on in vitro or animal investigations rather than direct human evidence. Despite the need for more definitive human studies, Hydrilla verticillata remains a promising plant-based ingredient due to its exceptional reported nutrient profile and the presence of potentially health-supportive phytochemicals.
Health conditions that Hydrilla verticillata may help support.
Body systems that Hydrilla verticillata may help support.
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