Guava

Guava (Psidium guajava L.): A Comprehensive Reference

1. Identity, Taxonomy, and Botanical Description

Taxonomically, Psidium guajava can be classified within the Plantae kingdom, Magnoliophyta division, Magnoliopsida class, Rosidae subclass, Myrtales order, Myrtaceae family, Myrtoideae subfamily, Myrteae tribe, Psidium genus, and Guajava species. The plant is commonly known by a wide range of vernacular names across its cultivation range, including guava, guayaba (Spanish), and goiaba (Portuguese). Guava (Psidium guajava L.) is an evergreen tree native to Mexico and Central America, and is a climacteric fruit that mainly grows in tropical and subtropical parts of various countries.

The adaptability of guava to various soils and environmental conditions facilitates relatively easy cultivation, yielding rapid fruit production. It is a tropical fruit extensively cultivated across various regions of the globe, encompassing countries like Egypt, India, Indonesia, Syria, Pakistan, Bangladesh, and South America, and it belongs to the Myrtaceae family.

The plant produces an edible berry fruit whose flesh can range from white to deep pink or red depending on cultivar. The soft, ripe guava fruit has a sweet musky aroma and a creamy texture, with flesh that can be white, pink, yellow, or red, and is packed with tiny, semi-hard edible seeds.

Common Forms and Preparations

All major parts of the guava plant are utilized medicinally and commercially. In ethnomedicine, the various parts of P. guajava — the stem, bark, fruits, leaves, and roots — are used in the treatment of diseases such as diarrhea, rheumatism, and diabetes, digestive problems, laryngitis, ulcers, malaria, cough, and bacterial infections. Many natives consume decoctions, infusions, and boiled preparations of P. guajava, either orally or topically, depending on the type of illness. Guava is commercially available in capsules, liquids, powders, and tablets.

2. Traditional and Historical Use

Mesoamerica and Mexico

Guava leaves have been used for medicinal purposes in Mexico since very remote times; their presence in historical documents on indigenous herbalism has been constant for at least five hundred years. This shrub used to be called by the ancient Mexicans as "xalxócotl," a word in Nahuatl that refers to a fruit that has a "hard and acid shell (xócotl) and a sandy texture (xalli)," due to its abundant seeds.

The folk use of guava has been documented in the indigenous groups of Mexican Indians: Maya, Nahuatl, Zapotec, and Popoluca. A decoction of the leaves is used to cure cough. According to communities of Nahuatl and Maya origin and Popoluca of the region of the Tuxtlas, Veracruz, they use a guava leaf decoction to treat digestive suffering associated with severe diarrhoea. This is a frequent disease in rainy weather.

In Mexico, P. guajava (Myrtaceae) is widely used to treat gastrointestinal and respiratory disturbances and is used as an anti-inflammatory medicine. Commonly, roots, bark, leaves, and immature fruits are used in the treatment of gastroenteritis, diarrhoea, and dysentery. Leaves are applied on wounds, ulcers, and for rheumatic pain, while they are chewed to relieve toothache.

The medicinal use of guava can also vary slightly according to the geographical location in the country; for example, while in southern Veracruz it has been reported that the plant is used to treat diarrhea, in the Huasteca Potosina it is also used to treat herpes, wounds, toothache, gastritis, and rashes.

The use of a water infusion prepared with the leaves of Psidium guajava L. as a popular therapeutic resource for the relief of some menstrual disorders that come with abdominal cramps and discomfort has been documented since ancient times both in Mexico and in other countries. In Mexican Traditional Medicine, the existence of abdominal pain in women is frequently associated with a "cold state of the uterus."

India and South Asia

For centuries, herbal remedies have been employed to address a variety of human ailments, and Psidium guajava Linn. (Myrtaceae), commonly known as guava, stands out as a noteworthy medicinal plant with significant pharmacological potential. In India, particularly in rural areas where access to conventional medicines can be limited, the various parts of the Psidium guajava plant, including its leaves, bark, roots, and fruit, have been harnessed for their therapeutic properties to tackle various health issues.

In particular, the leaf extract of guava has traditionally been used for the treatment of diabetes in East Asia and other countries. In traditional medicine, guava fruit can be eaten raw, and the roots can treat stomach problems, abdominal pain, dysentery, and diabetes; the leaves can treat diabetes, abdominal pain, rheumatism, antipyretic, stomachache, anthelmintic, cholera, vomiting, diarrhea, and enteritis.

Africa and Other Regions

Guava leaves have a traditional history of practice in African folk medicine for the management and treatment of diarrhea. The plant has been used in Africa and Asia to prevent and treat scurvy and to treat hypertension in western Africa, and ethnomedicinal reports document use of the plant in treating malaria.

Some of the countries with a long history of traditional medicinal use of guava include Mexico and other Central American countries including the Caribbean, Africa, and Asia.

Guava bark has been used medicinally as an astringent and to treat diarrhea in children, while the flowers have been used to treat bronchitis and eye sores and to cool the body. The fruit has been used as a tonic and laxative and for treatment of bleeding gums.

In the Pacific, Tahitians use the plant for conditions such as painful menstruation, miscarriages, uterine bleeding, and premature labor in women.

3. Key Constituents and Active Compounds

Phenolic Acids and Flavonoids

The leaves of the guava plant have been studied for their health benefits which are attributed to their plethora of phytochemicals, such as quercetin, avicularin, apigenin, guaijaverin, kaempferol, hyperin, myricetin, gallic acid, catechin, epicatechin, chlorogenic acid, epigallocatechin gallate, and caffeic acid.

The bioactive constituents extracted from P. guajava include phytochemicals such as gallic acid, casuariin, catechin, chlorogenic acid, rutin, vanillic acid, quercetin, syringic acid, kaempferol, apigenin, cinnamic acid, luteolin, quercetin-3-O-α-L-arabinopyranoside, morin, ellagic acid, guaijaverin, pedunculoside, asiastic acid, ursolic acid, oleanolic acid, methyl gallate, and epicatechin.

Within guava leaves, quercetin is recognized as the most potent antioxidant and is responsible for its spasmolytic activity.

Essential Oils and Terpenoids

Psidium guajava Linn. proves to be a valuable repository of essential nutrients along with bioactive compounds such as α-terpineol, β-caryophyllene (trans-caryophyllene), rutin, α-humulene, oleanolic acid, flavonoids, and quercetin.

Essential oil constituents include limonene, trans-caryophyllene, α-humulene, γ-muurolene, selinene, caryophyllene oxide, bisabolol, isocaryophyllene, δ-cadinene, α-copaene, α-cedrene, β-eudesmol, α-pinene, β-pinene, β-myrcene, linalool, α-terpineol, and eucalyptol. To identify the chemical components, Gas Chromatography–Mass Spectrometry was used to hydro-distillate the P. guajava leaves; the leaf essential oil contained a total of 27 components.

Macro- and Micronutrients in Fruit

Guava is a rich source of minerals and vitamins such as vitamin C, vitamin B, potassium, lycopene, manganese, iron, fibre, and calcium. Its vitamin C content is three to six times higher than that of orange, and its lycopene content twice that of tomato.

Guava fruits with pink pulp have been found to contain a high concentration of phenolic compounds and a considerable amount of carotenoids, particularly lycopene. These substances were mostly responsible for the antioxidant activity.

Tannins, Saponins, and Other Classes

Polyphenols, flavonoids, saponins, tannins, terpenoids, glycosides, flavones, cardiac glycosides, cardenolides, phlobatanins, steroids, and other classes of bioactive compounds have been identified from the leaves. The plant also contains bioactive compounds such as saponin, oleanolic acid, quercetin, catechin, epicatechin, rutin, and kaempferol. Additionally, the roots include tannins, leucocyanidins, gallic acid, and sterols.

The leaves host diverse bioactive compounds including phenols, flavonoids, terpenoids like gallic acid, and water-soluble tannins. This intricate chemical profile, particularly gallic acid, imparts the leaves with remarkable inhibitory effects against various pathogens, including bacteria and fungi. Compounds such as pyrocatechol, taxifolin, psiguadials, guaijaverin, and avicularin, among others, contribute to their hypoglycemic, antioxidant, anticancer, and antidiarrheal effects, showcasing the leaves' multifaceted therapeutic potential.

4. Established and Proposed Mechanisms of Action

Antidiarrheal and Antispasmodic Mechanisms

A survey of the literature shows P. guajava is mainly known for its antispasmodic and antimicrobial properties in the treatment of diarrhoea and dysentery. The therapeutic properties of the phytodrug are mainly attributed to the presence in the guava leaf extracts of five quercetin-derived flavonols that act as calcium antagonists at the intestinal smooth muscle and as antioxidants.

Guava buds and leaves were used to extract quercetin and quercetin-3-arabinoside, which, at doses of 1.6 g/mL, demonstrated a painkiller-like suppression of neurotransmitter release within the small intestine and caused a corresponding rise in muscle tone that gradually decreased. Asiatic acid, also isolated from the leaves, exhibited dose-dependent (10–500 µg/mL) spasmolytic action.

The inhibitory effects on gastrointestinal function exhibited by P. guajava extracts were comparable to those of established antidiarrheal agents such as morphine and loperamide. A P. guajava leaf aqueous extract was shown to increase water absorption in the colon's intestinal portion.

Antidiabetic and Glucose-Modulating Mechanisms

The active component of the aqueous guava leaf extract has been shown to inhibit alpha-glucosidase enzymes in vitro, demonstrating mechanisms for the reduction of postprandial blood glucose elevation and improvement of hyperglycemia, hyperinsulinemia, hypoadiponectinemia, hypertriglyceridemia, and hypercholesterolemia.

Various extracts prepared from guava (Psidium guajava) have been shown to inhibit sodium-dependent glucose cotransporter 1 (SGLT1)- and glucose transporter 2 (GLUT2)-mediated glucose transport in vitro (Caco-2 cells) and in vivo (C57BL/6N mice). In vitro studies have found that guava fruit extract can increase the expression of the GLUT4 gene and promote the entry of blood sugar into cells. At the same time, guava fruit extract can inhibit the formation of final glycated proteins (AGEs).

Antihypertensive Mechanisms

All tested guava extracts significantly inhibited ACE activity, scavenged free radicals (DPPH, ABTS•+, nitric oxide, and hydroxyl), chelated Fe²⁺, and inhibited Fe²⁺- and sodium nitroprusside-induced lipid peroxidation reactions in vitro. The antihypertensive activity has been related to the compounds rosmarinic acid, eugenol, carvacrol, catechin, and caffeic acid, which were found to be major constituents of guava extracts.

Antioxidant Mechanisms

P. guajava fruit has been shown to have an antioxidant effect by restoring enzymatic antioxidants and inhibiting the activation of nuclear factor-kappa B (NF-kB). The guava leaves extract exhibited antioxidant activity by inhibiting Fe²⁺-induced lipid peroxidation and scavenging free radicals (DPPH• and ABTS•⁺).

Anticancer Mechanisms (Preclinical)

Anticancer properties of guava have been discussed in the literature through various mechanisms, such as scavenging free radicals, regulation of gene expression, modulation of cellular signaling pathways, including those involved in DNA damage repair, cell proliferation, and apoptosis. These components exhibit diverse medicinal activities, encompassing anti-inflammatory, anti-cancer, anti-bronchitis, anti-proliferative, anti-tumor, anti-bacterial, and anti-diabetic effects.

5. Scientific Evidence by Area of Use

5.1 Diarrhea and Gastrointestinal Disorders

Human/Clinical Evidence: A systematic review was conducted of scientific articles published up to 2021, which included in vivo pre-clinical tests and clinical trials involving patients with acute infectious diarrhea to verify the antidiarrheal, antibacterial, and antispasmodic effects of galenic preparations or phytopharmaceuticals from P. guajava. Twenty (87%) of these reported heterogenic preclinical studies. Only three articles (13%) corresponded to clinical trials investigating the efficacy, dose, and safety of these preparations. Most studies reported positive results and significant mechanistic evidence from antibacterial, anti-motility, anti-secretory, and protective/anti-inflammatory perspectives. However, further studies are needed to define the clinical significance and safety treatment with P. guajava extracts.

A specific randomized, open-label clinical trial (published in PMC) evaluated guava leaf decoction (GLD) in adults. Diarrhoea is among the first ten causes of death and its treatment faces an increased threat of drug resistance. Previous studies on the guava leaf decoction (GLD) revealed its suitability for use in infectious diarrhoea of unknown etiology. The objective of the trial was to establish efficacy, dose, and safety of GLD prepared from the Indian Sardar variety in adults with acute infectious diarrhoea. The trial was an open efficacy randomized 5-day, parallel group multi-arm interventional study. Among 137 adults (18–60 years) suffering with acute diarrhoea, 109 were included (57% females, 43% males). Three doses of GLD (6-leaf, 10-leaf, and 14-leaf) were compared with controls receiving oral rehydration solution. Decrease in stool frequency and improvement in consistency were the outcomes measured.

In a clinical trial undertaken by Lozoya et al., compared to the placebo, patients receiving guava leaf capsules (quercetin-equivalent 1 mg per 500 mg capsule) experienced decreased duration of abdominal pain with no side effects. Quercetin, a major flavonoid and one of the most reported active constituents found in guava leaf, has been demonstrated to reduce capillary permeability in the abdominal cavity and inhibit intestinal movement in an in vitro model using guinea pig ileum. However, Birdi et al. demonstrated that quercetin alone had limited antidiarrheal activity and that the crude guava decoction was more effective.

Evidence Strength: The antidiarrheal evidence base is predominantly preclinical (animal models), with only a handful of small clinical trials. The mechanistic evidence is robust, but large, well-controlled randomized trials are lacking, rendering the clinical evidence preliminary to moderate.

5.2 Blood Glucose Regulation and Diabetes

Human/Clinical Evidence: In Japan, Guava Leaf Tea (Bansoureicha®, Yakult Honsha, Tokyo, Japan) containing the aqueous leaf extract from guava has been approved as one of the Foods for Specified Health Uses and is now commercially available.

Nineteen subjects aged over 40 years, with or without pre-diabetes, with an FBG level of 103.0 ± 14.3 mg/dL and a BMI of >22.0 were recruited. After overnight fasting for 11 hours, the subjects ingested 200 g of cooked rice as a loading carbohydrate together with a bottle (190 mL) of hot water at week 1 and then with the same volume of Guava Leaf Tea containing about 400 mg of GvEx at week 2. Blood glucose level was measured at 30-minute intervals for up to 150 min after ingestion.

A crossover clinical trial involving 20 hospitalized patients with T2DM was conducted to compare the potential of Guava Leaf Tea and voglibose (Basen®, Takeda Chemical Industries, Ltd., Tokyo, Japan) to reduce postprandial blood glucose elevation. A first long-term clinical trial was conducted to evaluate the effects of consecutive ingestion of Guava Leaf Tea with every meal for 12 weeks on the parameters of diabetes symptoms and safety. A second long-term clinical trial investigated the effects of consecutive ingestion of Guava Leaf Tea for 8 weeks in diabetic patients receiving therapy. Ingestion of the tea significantly decreased blood HbA1c% in diabetic patients who had initial values of >6.5% and were assessed to have abnormal control of blood glucose level.

A clinical trial reported that consumption of guava leaf tea improved postprandial insulin responses and lowered glycemic excursions in people who have trouble absorbing glucose. Additional clinical support is provided by a randomized controlled trial conducted in Taiwan, where drinking guava leaf tea daily for 12 weeks significantly reduced fasting blood glucose, HbA1c, and lipid levels in T2DM patients.

A double-blind, randomized clinical study published in Nutrients (2019) examined a guava fruit extract prepared by supercritical CO₂ extraction. A parallelized, randomized clinical study was conducted with young healthy adults. Thirty-one volunteers performed an oral glucose tolerance test (OGTT) in which the control group received a glucose solution and the intervention group received a glucose solution containing a guava fruit extract prepared by supercritical CO₂ extraction. The exact same extract was used for previous in vitro and in vivo experiments. Blood samples were collected prior to and up to two hours after glucose consumption to quantitate blood glucose and insulin levels. This clinical trial and previous in vitro and in vivo experiments confirmed the efficacy of the guava fruit extract in inhibiting intestinal glucose resorption, possibly in combination with reduced insulin secretion. Based on these findings, the development of food supplements or functional foods containing this extract appears promising for patients with diabetes and for the prevention of insulin resistance.

Evidence Strength: Several small-to-moderate human clinical trials have demonstrated meaningful reductions in postprandial blood glucose and HbA1c. The mechanistic basis (alpha-glucosidase inhibition, SGLT1/GLUT2 inhibition) is well-characterized in vitro and in vivo. The overall evidence is moderately supportive but constrained by small sample sizes and limited blinding in some trials.

5.3 Cardiovascular and Lipid Effects

Human/Clinical Evidence: A small randomized clinical trial published in the American Journal of Cardiology (1993) found that dietary supplementation with ripe guava fruit for 12 weeks resulted in significant reductions in blood pressure and cholesterol in patients with mild hypertension.

In clinical study dosing, 0.4 to 1 kg/day of guava fruit added to the diet for 4 to 12 weeks has been studied in healthy individuals and in patients with hypertension, and guava leaf tea 200 mL with every meal for 8 weeks was evaluated in a clinical study of subjects with hypercholesterolemia. Limited evidence from a few clinical trials suggests that the addition of guava fruit or guava leaf tea to the diet can improve lipid profile. Trials with fruit were conducted with a range of doses (0.4 to 1 kg/day) and durations (from 4 to 12 weeks).

Preclinical: Laboratory and animal studies suggest that guava leaf extracts may inhibit lipid peroxidation and improve endothelial function due to their high antioxidant content. However, while these findings are promising, they are limited in number and often involve small sample sizes or animal models. Larger, well-designed human trials are necessary to confirm these effects and to establish optimal dosages and preparations.

Evidence Strength: Evidence is preliminary. The available clinical trials are small, and the field lacks large, well-powered randomized controlled trials. The preclinical mechanistic data (ACE inhibition, radical scavenging, lipid peroxidation inhibition) are promising but have not been replicated at scale in humans.

5.4 Dysmenorrhea (Primary Menstrual Pain)

Human/Clinical Evidence: The abundant scientific research on the gastro-intestinal beneficial properties of products manufactured with this plant-based drug, Psidii guajavae folium, has consecutively shown that the extracts possess antimicrobial, anti-diarrheal, antispasmodic, anti-inflammatory, anti-oxidant, and neuro-sedative actions.

A randomized clinical trial by Doubova et al. (2007), published in the Journal of Ethnopharmacology, examined 6 mg/day of a guava leaf extract standardized to 6 mg of flavonol per day for 4 months, used to decrease menstrual pain intensity in a study of patients with primary dysmenorrhea.

A Cochrane systematic review on dietary supplements for dysmenorrhoea (published in PMC) included a comparison of guava with NSAIDs. The comparison found a mean difference of 1.19 (95% CI 0.42 to 1.96; one RCT, 155 women) in pain scores between NSAIDs and guava. This suggests that while guava showed a measurable effect on menstrual pain, NSAIDs appeared more effective in that single trial.

Evidence Strength: Moderate for menstrual pain reduction based on at least one RCT with 155 women and a standardized extract, but more trials are required. The Cochrane review highlighted guava as a candidate supplement in this domain but noted that evidence remains limited.

5.5 Antimicrobial Activity

Extracts from guava leaves have been studied for their biological activities, including anticancer, antidiabetic, antioxidant, antidiarrheal, antimicrobial, lipid-lowering, and hepatoprotection activities. Qualitative analysis of aqueous and organic extracts of guava leaves revealed the presence of phenolic acids, flavonoids, terpenoids, glycosides, and saponins, in which their presence is positively correlated with antimicrobial activity.

Around 27 antidiarrheal or antibacterial compounds have been isolated and identified from P. guajava, including benzophenone glycosides, terpenes, polysaccharides, phenols, and flavonoids. The majority of antimicrobial evidence remains from in vitro studies. Human clinical evidence in this area is limited to small pilot investigations.

Evidence Strength: The antimicrobial evidence is predominantly in vitro and animal-based. Well-controlled human trials specifically targeting antimicrobial endpoints are scarce.

5.6 Anticancer Properties

Multiple studies have highlighted the ability of P. guajava and its bioactive molecules, particularly those derived from its leaves, to selectively inhibit the growth of cancerous cells without harming normal cells. Researchers investigated the potential anticancer properties of guava seed polysaccharides against MCF-7 cells. Their findings indicated a significant dose-dependent inhibition of MCF-7 cell viability.

Evidence Strength: All anticancer evidence is from in vitro (cell culture) and animal studies. No human clinical trials on guava's anticancer effects have been reported in the reviewed literature. These findings are considered highly preliminary and cannot be extrapolated to human efficacy.

5.7 Oral and Dental Health

The guava leaf extract has been investigated for dental plaque and gingivitis applications. One application reviewed in clinical dosage literature involves a 0.15% mouthrinse, 10 mL swished twice daily for 30–90 days after professional cleaning and daily brushing/flossing. Evidence in this domain is based on a small number of clinical trials, and the research base remains limited.

6. Body Systems and Health Areas of Association

The available literature shows that guava is associated with the following conditions: gastrointestinal infections, malaria, respiratory infections, oral/dental infections, skin infections, diabetes, cardiovascular/hypertension, cancer, malnutrition, women's health problems, pain, fever, liver problems, and kidney problems.

In vitro and in vivo studies have demonstrated that P. guajava possesses pharmacological activities such as antidiabetic, antidiarrhoeal, hepatoprotective, anticancer, antioxidant, anti-inflammatory, antiestrogenic, and antibacterial activities, which support its traditional uses.

7. Dosage Forms and Dosages Reported in Clinical Studies

The following dosages represent those actually reported in clinical study literature. They should not be interpreted as established recommended doses for self-administration.

• Diarrhea — capsule form: Capsules containing 500 mg of a phytodrug developed from guava leaves (standardized concentration of flavonoids, estimated as 1 mg of quercetin per 500 mg) every 8 hours for 3 days was used in one clinical trial of adults with acute diarrhoeic disease; 10 mL of Psidium guajava tincture dissolved in water taken every 8 hours has also been used in a study of adults with acute diarrhea.
• Diarrhea — leaf decoction: Among 137 adults (18–60 years), three doses of GLD (6-leaf, 10-leaf, and 14-leaf) were compared with controls over a 5-day study.
• Dysmenorrhea — oral extract: 6 mg/day of a guava leaf extract standardized to 6 mg of flavonol per day for 4 months was used to decrease menstrual pain intensity in a study of patients with primary dysmenorrhea.
• Hyperlipidemia and hypertension — fruit: 0.4 to 1 kg/day of guava fruit added to the diet for 4 to 12 weeks has been studied in healthy individuals and in patients with hypertension.
• Hypercholesterolemia — guava leaf tea: Guava leaf tea 200 mL with every meal for 8 weeks was evaluated in a clinical study of subjects with hypercholesterolemia.
• Postprandial blood glucose — guava leaf tea: Subjects ingested 190 mL of Guava Leaf Tea containing about 400 mg of guava leaf extract (GvEx) along with a standard carbohydrate meal in a crossover study.
• Oral health — mouthrinse: A 0.15% mouthrinse, 10 mL swished twice daily for 30–90 days was studied in the context of gingivitis and plaque control.

Guava is commercially available in capsules, liquids, powders, and tablets.

8. Safety Considerations and Drug Interactions

Acute and Subacute Toxicology

Numerous research studies have assessed the guava's (P. guajava) safety and toxicology. Using methanolic and ethanolic extracts of guava leaves, acute toxicity testing revealed that dosages of up to 5000 mg/kg in rodents did not result in death, suggesting a high safety margin. Studies on chronic toxicity conducted over a period of 90 days showed that dosages up to 200 mg/kg/day were safe and did not significantly alter histological, hematological, or biochemical markers. Higher doses (400 mg/kg/day) were shown to cause liver toxicity, which included tissue destruction and elevated biomarkers, suggesting that long-term high-dose use may be dangerous.

In an acute toxicity study, no mortality or signs of toxicity were recorded; hence, the median lethal dose (LD₅₀) of the Psidium guajava bark extract is greater than 5000 mg/kg body weight. Histopathological analyses showed minor liver inflammation in females treated at the highest dose (1000 mg/kg) in the subacute (28-day) study.

Approved Safety Profile — Japan

Previous in vitro studies and investigations using animal models have demonstrated that guava leaf tea and its extract induce neither toxicity nor mutagenicity. It is suggested that guava leaf tea containing extract is a useful and harmless food for treating pre-diabetic and diabetic patients.

Drug Interactions

Hypoglycemic agents: Because guava lowers blood sugar, people taking insulin or glucose-lowering medications need to monitor their levels carefully.

Metoclopramide and CYP enzyme interactions: Psidium guajava enhanced the oral exposure of metoclopramide in rabbits, likely by the inhibition of P-glycoprotein-mediated efflux during intestinal absorption and inhibition of the P450 enzyme system during metabolism, suggesting that the combined use of Psidium guajava or a Psidium guajava-containing diet with metoclopramide may require close monitoring for potential drug–diet interactions. This was a preclinical (rabbit) study; its direct clinical significance in humans has not been confirmed.

Iron absorption: Tannins in guava can reduce iron absorption; it is advisable to separate guava preparations from iron supplements by at least 2–3 hours.

General Observations

Little is known regarding the therapeutic activity of guava leaf extract in human clinical trials as well as its underlying therapeutic mechanisms and safety at pharmacological doses beyond food consumption. While the fruit is consumed widely as a food without reported adverse effects in typical dietary quantities, concentrated leaf extracts and standardized phytodrug preparations have not been subjected to long-term large-scale safety studies in humans. The preclinical toxicology data suggest a favorable acute safety profile but indicate potential organ-level effects at sustained high doses in animal models.

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