Nutrition Diet: What Teas Are Not Safe for Your Health?

October 26, 2025 •

4 min read

According to a study published in the journal Clinical Toxicology, the raw form of the herb aconite is extremely toxic when consumed and can be fatal. Understanding what teas are not safe is critical for anyone looking to maintain a healthy and safe diet and avoid potential harm from certain ingredients or contaminants.

Quick Summary

Certain herbal and caffeinated teas can pose significant health risks, including severe liver damage from ingredients like comfrey, dangerous interactions with medication, and toxicity from contaminants or excessive consumption.

Key Points

Avoid Highly Toxic Herbs: Teas containing comfrey, pennyroyal, kava, sassafras, aconite, and chaparral are dangerous and should not be consumed, as they can cause severe liver or organ damage.
Be Mindful of Drug Interactions: St. John's Wort interacts negatively with many prescription medications, including contraceptives and antidepressants, and should only be used under medical supervision.
Use Caution with Certain Health Conditions: Individuals with high blood pressure, heart disease, or iron deficiency should be cautious with licorice root and high consumption of green or black teas, which can worsen symptoms.
Limit Caffeine Intake: Excessive consumption of caffeinated teas like black, green, and oolong can cause anxiety, insomnia, and irregular heartbeats.
Consider Contamination Risks: Some teas, especially non-organic imported brands, may contain harmful heavy metals or pesticide residues. Using organic, loose-leaf tea and filtered water can reduce this risk.
Choose Plastic-Free Tea Bags: Many teabags release billions of microplastic particles into your beverage when steeped in hot water. Opt for plastic-free or loose-leaf options to avoid this.

While the comforting ritual of a warm cup of tea is a staple for many, not all teas are created equal. The world of herbal infusions is vast, and certain plants harbor potent compounds that can be harmful when ingested. The following guide highlights potentially dangerous teas, identifies risks under specific health conditions, and reveals hidden dangers from contaminants and processing.

Potentially Toxic Herbal Teas to Avoid

Many people incorrectly assume that because a substance is 'natural' or 'herbal', it is automatically safe. However, many plants contain compounds that can cause serious or fatal health issues.

Comfrey Tea (Symphytum officinale)

Comfrey is perhaps one of the most notorious examples of a dangerous herbal tea. It contains naturally occurring plant toxins called pyrrolizidine alkaloids (PAs).

Liver Damage: When ingested orally, PAs are known to cause severe, irreversible liver damage, which can lead to liver failure and death.
Banned Oral Use: Due to these severe risks, oral comfrey preparations have been banned or restricted in many countries, and its use is strongly discouraged.

Pennyroyal Tea (Mentha pulegium)

Historically used as an abortifacient (a substance used to induce abortion), the essential oil of pennyroyal is highly toxic and can be fatal, even in small doses.

Active Toxin: The toxic compound is pulegone, which is particularly damaging to the liver.
Symptoms: Ingestion can cause severe illness, including multi-organ failure, seizures, and death.
Warning: The essential oil should never be ingested. Even the tea is not recommended due to potential liver toxicity.

Kava Kava (Piper methysticum)

Kava is used for anxiety and relaxation but has been linked to severe liver damage in some users, sometimes requiring liver transplants.

Liver Risk: The risk is highest with high doses, prolonged use, or poor-quality supplements, and is exacerbated by alcohol or pre-existing liver conditions.
Drug Interactions: Kava can also interact dangerously with medications, especially those that affect the liver, such as acetaminophen.

Other Highly Risky Herbal Teas

Several other herbs should be avoided due to their toxic properties or lack of safety data:

Aconite (Monkshood): Extremely poisonous and has caused deaths from cardiac and respiratory failure.
Chaparral: Linked to severe liver damage.
Sassafras: Contains safrole, a known carcinogen.
Ephedra (Ma Huang): Contains stimulants that can increase heart rate and blood pressure, potentially causing dangerous cardiac events.

Teas to Limit or Avoid Under Specific Conditions

For many common teas, safety is a matter of moderation and considering individual health factors.

Licorice Root Tea (Glycyrrhiza glabra)

While a popular flavoring, excessive intake of licorice root can cause serious health issues, particularly for people with high blood pressure.

Hypertension: The active compound, glycyrrhizin, can lead to increased blood pressure, low potassium levels (hypokalaemia), and fluid retention.
Safe Intake: Limiting intake is crucial, and it should be avoided entirely by individuals with hypertension, heart disease, or during pregnancy.

St. John's Wort Tea (Hypericum perforatum)

Known for its use in treating depression, St. John's wort has powerful interactions with many prescription medications.

Serious Interactions: It can render birth control pills ineffective, weaken the effects of immunosuppressants and chemotherapy, and cause dangerous interactions with antidepressants, leading to serotonin syndrome.
Warning: It is essential to consult a doctor before consuming if taking any prescription drugs.

Caffeinated Teas (Green, Black, Oolong)

Traditional teas from the Camellia sinensis plant are generally safe, but overconsumption can lead to negative side effects primarily due to caffeine and tannins.

Caffeine Overload: High intake can cause anxiety, insomnia, headaches, and an irregular heartbeat.
Iron Absorption: Tannins can inhibit iron absorption, posing a risk for individuals with anemia or iron deficiencies.
Oxalates: Some teas contain oxalates, which in very high, rare quantities can contribute to kidney stones.

Hidden Dangers: Contamination and Processing

Even seemingly harmless teas can present risks due to the way they are grown, processed, and packaged.

Heavy Metal Contamination

Tea plants can absorb heavy metals like lead, aluminum, and cadmium from contaminated soil.

Source: Contamination is a particular concern with tea imported from regions with poor environmental regulations.
Higher Risk: Longer steeping times can increase the leaching of these metals into the brew.

Microplastics from Tea Bags

Many commercial tea bags and sachets are made from plastics like polyethylene terephthalate (PET) or polylactic acid (PLA).

Release of Particles: Studies show that billions of microplastic and nanoplastic particles can be released into a single cup of tea brewed with a plastic bag.
Alternative: To avoid this, use teas packaged in plastic-free bags or brew with loose-leaf tea.

Comparison Table: Safe vs. Unsafe Herbal Tea Ingredients


Feature	Potentially Unsafe Herbs	Generally Safe Herbs (in moderation)
Liver Risk	High (Comfrey, Kava, Pennyroyal)	Low (e.g., Peppermint, Ginger)
Drug Interactions	High (St. John's Wort, Kava, Ephedra)	Low (Always check with a doctor)
Pregnancy/Hormone Effects	High (Pennyroyal, Licorice, Sage, Nettle)	Low (e.g., Ginger, Mint - consult doctor)
Toxicity	High (Aconite, Sassafras, Chaparral)	Very Low/None
Regulation	Oral use banned/restricted (Comfrey, Kava in some places)	Widely available and considered safe

Conclusion: Navigating Tea Safely

For most people, the daily cup of tea poses no threat. However, the world of herbal infusions is not without its hazards. Highly toxic herbs like comfrey and pennyroyal should be completely avoided, and teas like licorice root and St. John's wort require caution depending on your health status and medications. Environmental contaminants and processing materials also present hidden risks that can be minimized by choosing organic loose-leaf tea and filtered water. As with any dietary addition, particularly potent herbal products, consultation with a healthcare professional is wise, especially for pregnant women or individuals with chronic health conditions.

For more detailed information on herbal interactions, consult reliable sources like the NIH's LiverTox database.

Frequently Asked Questions

Herbal teas such as comfrey, kava kava, and pennyroyal are known to be particularly toxic to the liver. Comfrey contains pyrrolizidine alkaloids, and kava has been linked to liver damage severe enough to require transplants.

Some herbal teas pose risks during pregnancy due to their effects on hormones or the uterus. Healthcare providers recommend avoiding teas with ingredients like licorice root, pennyroyal, sage, and nettle. It is best to consult a doctor before drinking any herbal tea during pregnancy.

While drinking green tea is generally safe, consuming high-dose green tea extracts can be linked to liver damage, particularly in individuals with certain genetic variations. These supplements are not regulated and can contain toxic levels of compounds.

Licorice root tea is known to raise blood pressure and cause low potassium levels due to the compound glycyrrhizin. Individuals with hypertension or heart issues should avoid or limit consumption of licorice tea.

Yes, some conventional tea bags are made of plastic or treated with a chemical called epichlorohydrin. When steeped in hot water, these can release microplastic particles and other toxins into your tea. Choosing plastic-free or loose-leaf options is a safer alternative.

St. John's Wort has significant interactions with many prescription drugs, including antidepressants, birth control, and HIV medications. Kava and some other herbs can also interact with medicines. Always inform your doctor or pharmacist about any herbal supplements you take.

Excessive intake of black tea, defined as more than four or five cups a day, can cause side effects related to its high caffeine content. These include anxiety, restlessness, insomnia, increased heart rate, and elevated blood pressure.