Toxicology

Overview

The toxicological safety of Ilex guayusa has been investigated in extensive preclinical and clinical studies. This page provides a detailed overview of all available toxicological data for scientific and regulatory professionals.

Regulatory Status

• GRAS status (USA): Generally Recognized as Safe (GRN-835)
• EU Novel Food: Approved in 2017 following EFSA evaluation
• Historical use: Centuries of safe use by indigenous peoples

Test Substance

Most toxicological studies used standardized Guayusa leaf extracts with the following composition:

• Caffeine: 2.0-3.5% (w/w)
• Chlorogenic acids: 8-12% (w/w)
• Total Polyphenols: 15-20% (w/w)
• Moisture: <5%
• Heavy metals: Below detection limit

Acute Toxicity

Oral Acute Toxicity (Rats)

An acute oral toxicity study according to OECD Guideline 423 was conducted in Sprague-Dawley rats:

Study Design

• Species: Sprague-Dawley rats
• Sex: Female (n=6)
• Dose: 2,000 mg/kg body weight (limit test)
• Application: Single oral gavage
• Observation period: 14 days

Results

• Mortality: 0/6 (no deaths)
• Clinical signs: No toxic symptoms
• Body weight: Normal weight gain
• Food consumption: Unchanged
• Macroscopic pathology: No abnormalities

LD₅₀ Value

Based on the limit test:

• LD₅₀ (oral, rat): >2,000 mg/kg body weight
• Classification: Not acutely toxic (GHS category 5 or not classified)

Comparison with Caffeine

For comparison: The LD₅₀ of pure Caffeine in rats is:

• Caffeine LD₅₀ (oral, rat): 192 mg/kg
• Guayusa extract LD₅₀: >2,000 mg/kg
• Safety factor: >10 times safer than pure Caffeine

This suggests that other components in Guayusa (particularly Polyphenols) modulate the acute toxicity of Caffeine or that matrix effects reduce bioavailability.

Daily caffeine cutoff

For most users, timing matters as much as total amount. Use this calculator to estimate a practical last-intake window.

Subchronic Toxicity

90-Day Study (Rats)

A 90-day oral toxicity study according to OECD Guideline 408 was conducted in Sprague-Dawley rats:

Study Design

Parameters Investigated

• Clinical observations: Daily
• Body weight: Weekly
• Food consumption: Weekly
• Ophthalmology: Before study and before sacrifice
• Hematology: Day 45 and 90
• Clinical chemistry: Day 45 and 90
• Urinalysis: Day 88-90
• Organ weights: At sacrifice
• Histopathology: Over 40 tissues/organs

Results

Mortality and Clinical Signs

• Mortality: No treatment-related deaths
• Clinical signs: No toxic symptoms
• Ophthalmology: No abnormalities

Body Weight and Food Consumption

• Body weight: No significant differences between groups
• Weight gain: Normal in all groups
• Food consumption: Unchanged
• Feed efficiency: No impairment

Hematology

No treatment-related changes in:

• Erythrocytes, hemoglobin, hematocrit
• Leukocytes and differential blood count
• Platelets
• Coagulation parameters (PT, aPTT)

Clinical Chemistry

No treatment-related changes in:

• Liver enzymes: ALT, AST, ALP, GGT
• Kidney parameters: Creatinine, urea, uric acid
• Electrolytes: Na⁺, K⁺, Cl⁻, Ca²⁺, PO₄³⁻
• Metabolism: Glucose, cholesterol, triglycerides
• Proteins: Total protein, albumin, globulins

Urinalysis

• pH, specific gravity: Unchanged
• Protein, glucose: No abnormalities
• Sediment: Normal

Organ Weights

No treatment-related changes in absolute or relative organ weights (liver, kidneys, heart, spleen, thymus, adrenal glands, gonads, brain).

Histopathology

Detailed histopathological examination of over 40 tissues and organs showed:

• No treatment-related lesions
• No evidence of organ damage
• No proliferative changes
• Normal tissue architecture in all groups

NOAEL and LOAEL

Human Equivalent Dose (HED)

Conversion of the NOAEL to human equivalent dose:

• NOAEL (rat): 1,000 mg/kg/day
• Body weight (human): 60 kg (assumption)
• Conversion factor: 6.2 (rat → human, FDA guidance)
• HED: 1,000 ÷ 6.2 = 161 mg/kg/day
• Absolute dose (60 kg): 9,660 mg/day (~10 g/day)

This corresponds to approximately 300-500 cups of Guayusa tea per day – far beyond any realistic consumption amount.

Chronic Toxicity

Specific chronic toxicity studies (6-12 months) with Guayusa extract have not been conducted. However, the following data provide indications of long-term safety:

Historical Use

• Duration: Centuries-long use by indigenous peoples
• Consumption pattern: Daily intake, often multiple times daily
• Reports: No documented chronic toxicities
• Ethnobotanical Literature: No evidence of long-term damage

Caffeine Long-Term Studies

Since Caffeine is the main active ingredient, long-term studies on caffeine are relevant:

• Epidemiological Studies: No increased cancer risk with moderate consumption
• Cardiovascular: No increased mortality at 3-5 cups/day
• Liver: Protective effects against cirrhosis and liver cancer
• Neurodegeneration: Possible protection against Parkinson's and Alzheimer's

Polyphenol Long-Term Safety

Chlorogenic acids and other Polyphenols in Guayusa:

• Green Tea: Centuries of safe use of similar Polyphenols
• Coffee: Chlorogenic acids as main Polyphenols, no chronic toxicity
• Antioxidant Effects: More protective than toxic

Genotoxicity

A comprehensive battery of Genotoxicity tests was conducted to assess the mutagenic and clastogenic potential of Guayusa:

Bacterial Reverse Mutation Test (Ames Test)

Study Design

• Guideline: OECD 471
• Strains: Salmonella typhimurium TA98, TA100, TA1535, TA1537; E. coli WP2 uvrA
• Doses: 50, 150, 500, 1,500, 5,000 μg/plate
• Metabolic Activation: With and without S9 mix
• Positive Controls: 2-Nitrofluorene, sodium azide, 9-aminoacridine, 2-aminoanthracene

Results

Conclusion: Guayusa extract is not mutagenic in bacteria.

In Vitro Chromosome Aberration Test

Study Design

• Guideline: OECD 473
• Cells: Human peripheral blood lymphocytes
• Doses: 125, 250, 500, 1,000, 2,000 μg/mL
• Metabolic Activation: With and without S9 mix
• Treatment Duration: 3 hours (with S9), 24 hours (without S9)
• Positive Control: Mitomycin C, cyclophosphamide

Results

• Structural Aberrations: No increase at all doses
• Numerical Aberrations: No polyploidy or aneuploidy
• Mitotic Index: Unchanged (no cytotoxicity)
• Conclusion: Not clastogenic (no chromosomal damage)

In Vivo Micronucleus Test

Study Design

• Guideline: OECD 474
• Species: Mice (CD-1)
• Sex: Male (n=5/group)
• Doses: 500, 1,000, 2,000 mg/kg (single oral administration)
• Sampling: Bone marrow, 24 and 48 hours after administration
• Positive Control: Cyclophosphamide

Results

*Significantly increased vs. control (p<0.001). PCE = polychromatic erythrocytes.

Conclusion: Guayusa extract does not induce micronuclei in vivo and is therefore not genotoxic.

Overall Genotoxicity Assessment

Based on the totality of the data:

• Mutagenicity: Negative (Ames test)
• Clastogenicity: Negative (chromosome aberration test)
• In vivo Genotoxicity: Negative (micronucleus test)
• Overall assessment: Not genotoxic

Reproductive Toxicology

Specific reproductive and developmental toxicity studies with Guayusa extract have not been published in peer-reviewed journals. However, the following data provide indications:

90-Day Study: Reproductive Organs

Reproductive organs were examined in the 90-day study:

• Organ Weights: Testes, epididymides, ovaries, uterus – no changes
• Histopathology: Normal spermatogenesis, no lesions in reproductive organs
• Hormonal Parameters: Not investigated

Caffeine Reproductive Toxicity

Since Caffeine is the main active ingredient, caffeine data are relevant:

Fertility

• Human Data: Moderate Caffeine consumption (&lt;300 mg/day) has no negative impact on fertility
• Animal Studies: NOAEL for fertility: ~80 mg/kg/day (rats)

Pregnancy

• Recommendation: Limit to &lt;200 mg Caffeine/day during pregnancy (EFSA, FDA)
• Placental Transfer: Caffeine crosses the placenta
• Fetal Metabolism: Reduced (CYP1A2 not expressed)
• Risks with High Consumption: Low birth weight, preterm birth (at &gt;300 mg/day)

Lactation

• Milk Transfer: Caffeine passes into breast milk (~1% of maternal dose)
• Recommendation: &lt;300 mg/day during lactation
• Infant Effects: Irritability, sleep disturbances with very high maternal consumption

Recommendations

Based on Caffeine content (2-3.5% in Guayusa):

• Pregnancy: Limit to 1-2 cups/day (equivalent to ~100-140 mg Caffeine)
• Lactation: Limit to 2-3 cups/day
• Children: Not recommended for children under 12 years

Allergenicity and Sensitization

Skin Sensitization

Specific skin sensitization studies (e.g., Local Lymph Node Assay) with Guayusa have not been published.

Indirect Evidence

• Historical Use: No reports of allergic skin reactions
• Cross-reactivity: Possible cross-reactivity with other Ilex species (e.g., Yerba Mate) in case of allergy
• Polyphenols: Chlorogenic acids are not known as skin sensitizers

Oral Allergenicity

Guayusa does not contain any known major allergens:

• Protein Content: Very low in aqueous extracts (&lt;1%)
• Known Allergens: No specific allergens identified
• Cross-reactivity: Theoretically possible with other Aquifoliaceae

Pollen Allergy

• Flowers: Extremely rare (see botany page)
• Pollen Exposure: Negligible
• Risk: Very low

Anaphylaxis

No cases of anaphylaxis due to Guayusa consumption have been documented:

• Literature: No reports in medical literature
• Spontaneous Reports: No known cases
• Risk Assessment: Very low risk

Recommendations

• First consumption: Caution with known allergy to other Ilex species
• Symptoms: In case of rash, itching, shortness of breath → discontinue use and consult a physician
• Cross-reactivity: Possible cross-reactivity with Yerba Mate should be considered

Drug Interactions

Guayusa can interact with certain medications, mainly through Caffeine and Polyphenols:

Cytochrome P450 Interactions

CYP1A2 Substrates

Caffeine is primarily metabolized by CYP1A2. Drugs that inhibit or induce CYP1A2

CYP1A2 Inhibitors (increase Caffeine levels)

CYP1A2 Inducers (reduce Caffeine levels)

Pharmacodynamic Interactions

Stimulants

Additive stimulating effects with:

• Ephedrine: Increased risk of hypertension, tachycardia
• Pseudoephedrine: Additive sympathomimetic effects
• Amphetamines: Enhanced CNS stimulation
• MDMA (Ecstasy): Increased risk of cardiovascular complications

Bronchodilators

• Theophylline: Caffeine is structurally related; additive effects and toxicity possible
• β2-Agonists: Additive cardiovascular effects (tachycardia)

Antihypertensives

• β-Blockers: Caffeine can partially antagonize blood pressure-lowering effects
• Calcium antagonists: Possible reduction of efficacy

Antidiabetics

• Insulin: Caffeine can influence blood sugar regulation
• Oral antidiabetics: Chlorogenic acids can lower blood sugar (synergistic)

Polyphenol Interactions

Iron Absorption

• Mechanism: Polyphenols chelate iron and reduce absorption
• Effect: 40-60% reduction of non-heme iron absorption
• Recommendation: Do not consume Guayusa simultaneously with iron supplements (2-hour interval)

Other Minerals

• Calcium: Slight reduction in absorption
• Zinc: Possible reduction in absorption
• Magnesium: Minimal effect

Recommendations

• CYP1A2 inhibitors: Reduce Caffeine intake to 1-2 cups/day
• Stimulants: Avoid combination or use under medical supervision
• Theophylline: Close monitoring of Theophylline levels
• Iron supplements: 2-hour interval from Guayusa consumption
• Pregnancy: Inform physician about Caffeine consumption

Clinical Safety

Krieger et al. (2016) - Human Study

The clinical safety of Guayusa was investigated in a randomized, double-blind study in 40 healthy adults:

Safety Parameters

• Adverse events: No serious side effects
• Vital signs: No clinically relevant changes
• ECG: No abnormalities
• Laboratory parameters: All within normal range

Reported Side Effects

All side effects were mild and self-limiting. Interestingly, Guayusa shows a tendency towards less nervousness than synthetic Caffeine, possibly due to L-Theanine synergy.

Post-Marketing Surveillance

Since market introduction in Europe and the USA (2012-2017):

• Spontaneous reports: No serious adverse effects reported
• Allergic reactions: Very rare (&lt;0.01%)
• Gastrointestinal complaints: Occasional (1-10%), mostly mild

Contraindications

• Caffeine hypersensitivity: Absolutely contraindicated
• Severe cardiac arrhythmias: Caution advised
• Severe anxiety disorders: May worsen symptoms
• Pregnancy: Limitation to &lt;200 mg Caffeine/day recommended

Warnings

• Children and adolescents: Not recommended for children &lt;12 years
• Caffeine-sensitive individuals: Start with low dose
• Evening consumption: May impair sleep
• Dehydration: Drink sufficient water (diuretic effect)

Overdose

Symptoms of Caffeine overdose (&gt;400 mg caffeine):

• CNS: Nervousness, tremor, insomnia, headache
• Cardiovascular: Tachycardia, palpitations, hypertension
• Gastrointestinal: Nausea, vomiting, diarrhea
• Severe overdose (&gt;1,000 mg): Arrhythmias, seizures, rhabdomyolysis

Treatment: Symptomatic, activated charcoal in acute ingestion, supportive measures.