A practical, reference to commonly used herbs, their safety considerations, and potential side effects.
Herbs have been used for centuries across cultures as food, medicine, and ritual. Today, they remain a cornerstone of natural wellness, culinary tradition, and holistic health practices. While many herbs are gentle and widely considered safe, it is important to remember that “natural” does not automatically mean harmless. Herbs contain active compounds that can interact with medications, affect underlying health conditions, and produce side effects when used improperly or in excess. Factors such as age, pregnancy, chronic illness, and prescription drug use all influence how an herb affects the body. This guide offers a practical, alphabetical reference to commonly used herbs, their safety considerations, and potential side effects, empowering you to make informed, thoughtful choices about incorporating herbs into your daily life.
| Common Name | Scientific Name | Safety Guidelines | Possible Side Effects |
|---|---|---|---|
| Aloe Vera | Aloe barbadensis miller | Topical use is generally safe. Avoid oral use of latex (inner leaf) during pregnancy, with kidney conditions, or with laxatives and diabetes medications. | Skin irritation (topical), severe cramping, diarrhea, electrolyte imbalance, kidney damage (oral latex) |
| Angelica | Angelica archangelica | Avoid during pregnancy (uterine stimulant). Use caution with blood thinners. Avoid prolonged sun exposure during use. | Photosensitivity, skin burns, GI upset, possible uterine stimulation |
| Arnica | Arnica montana | For external use only. Never apply to broken skin or open wounds. Avoid with blood thinners. Oral use is toxic except in homeopathic dilutions. | Skin irritation, contact dermatitis, allergic reaction; oral use causes serious toxicity |
| Ashwagandha | Withania somnifera | Avoid during pregnancy and with thyroid medications or immunosuppressants. Use for no more than 3 months continuously. | Digestive upset, drowsiness, thyroid hormone fluctuation |
| Astragalus | Astragalus membranaceus | Avoid with immunosuppressant drugs. Not recommended for autoimmune conditions. | Mild digestive issues, possible immune overstimulation |
| Basil | Ocimum basilicum | Safe in culinary amounts. Medicinal doses should be avoided during pregnancy. | Rarely, low blood sugar with high doses; possible blood-thinning effect |
| Black Cohosh | Actaea racemosa | Avoid with liver conditions or hormone-sensitive cancers. Limit use to 6 months. | Headache, nausea, liver toxicity (rare), stomach upset |
| Black Haw | Viburnum prunifolium | Avoid during pregnancy (uterine relaxant historically used to prevent miscarriage but requires medical supervision). Use caution with blood thinners and aspirin-sensitive individuals. | Nausea, tinnitus, salicylate sensitivity reactions, GI upset |
| Bladderwrack | Fucus vesiculosus | Avoid with thyroid disorders, iodine sensitivity, and thyroid medications. Do not use during pregnancy. Avoid if sourced from polluted waters due to heavy metal risk. | Thyroid disruption, iodine toxicity, heavy metal accumulation, acne |
| Bloodroot | Sanguinaria canadensis | Extremely toxic in high doses. Internal use should only be under qualified supervision. Avoid during pregnancy. Avoid topical products with high concentrations (escharotic risk). | Nausea, vomiting, tissue destruction (topical), liver damage, death in overdose |
| Boneset | Eupatorium perfoliatum | Avoid during pregnancy. Do not use long-term. Contains pyrrolizidine alkaloids; limit use to acute short-term illness. | Nausea, vomiting, liver damage with prolonged use, allergic reaction (ragweed family) |
| Borage | Borago officinalis | Avoid during pregnancy and with liver conditions. Contains pyrrolizidine alkaloids; limit long-term use. | Liver damage with prolonged use, mild GI upset |
| California Poppy | Eschscholzia californica | Avoid during pregnancy and with sedatives, MAOIs, and antidepressants. Not related to opium poppy but has mild sedative properties. | Drowsiness, dizziness, mild GI upset |
| Calendula | Calendula officinalis | Avoid during pregnancy. Use caution with ragweed allergy. | Allergic skin reactions, contact dermatitis |
| Cayenne | Capsicum annuum | Avoid topical use near eyes or broken skin. Use caution with blood thinners and ACE inhibitors. | Burning sensation, GI irritation, sweating, runny nose |
| Chamomile | Matricaria chamomilla | Use caution with ragweed or daisy allergies. May enhance sedatives and blood thinners. | Allergic reactions, drowsiness, rare anaphylaxis |
| Chasteberry (Chaste Tree) | Vitex agnus-castus | Avoid during pregnancy and with hormone therapies or dopamine-related medications. | Headache, nausea, acne, menstrual cycle disruption |
| Cinnamon | Cinnamomum verum | Cassia cinnamon contains coumarin; prefer Ceylon variety. Avoid high doses with diabetes medications. | Mouth sores with excess use, liver stress (cassia), blood sugar drops |
| Coleus Forskohlii | Coleus forskohlii | Avoid with blood pressure medications, blood thinners, and heart medications. Use caution before surgery. | Low blood pressure, increased heart rate, headache, GI upset |
| Coltsfoot | Tussilago farfara | Avoid during pregnancy and breastfeeding. Contains pyrrolizidine alkaloids; long-term use is not recommended. Avoid with liver conditions. | Liver damage, hepatotoxicity with prolonged use, possible carcinogenic risk |
| Comfrey | Symphytum officinale | Topical use only on intact skin for short periods. Internal use is not recommended due to pyrrolizidine alkaloids. Avoid during pregnancy. | Liver damage (internal use), skin irritation, carcinogenic risk with long-term internal use |
| Dandelion | Taraxacum officinale | Use caution with diuretics, lithium, and antibiotics. Avoid with ragweed allergy. | Heartburn, diarrhea, allergic reactions |
| Dandelion Root | Taraxacum officinale radix | Use caution with diuretics, bile duct obstruction, and gallstones. Avoid with ragweed allergy. Separate from oral medications as it may affect absorption. | Heartburn, diarrhea, allergic reaction, increased bile flow |
| Dang Gui (Dong Quai) | Angelica sinensis | Avoid during pregnancy and with blood thinners, hormone-sensitive conditions, and hormone therapies. Avoid prolonged sun exposure during use. | Photosensitivity, heavy menstrual bleeding, GI upset, hormonal effects |
| Echinacea | Echinacea purpurea | Avoid with autoimmune disorders and immunosuppressants. Limit continuous use to 8 weeks. | Nausea, rash, allergic reaction, GI discomfort |
| Elderberry | Sambucus nigra | Raw berries, bark, and leaves are toxic. Use only prepared extracts. Avoid with immunosuppressants. | Nausea, vomiting (raw plant), possible immune overstimulation |
| Ephedra (Ma Huang) | Ephedra sinica | Banned by the FDA for use in dietary supplements in the US. Avoid with heart conditions, high blood pressure, diabetes, thyroid disorders, and stimulants. Extremely high risk profile. | Heart attack, stroke, seizure, death; nervousness, insomnia, elevated blood pressure |
| Eucalyptus | Eucalyptus globulus | Never ingest eucalyptus oil; it is toxic internally. Do not apply near the face or nose of infants or young children. Use caution with liver conditions and diabetes medications. | Nausea, vomiting, diarrhea (ingestion), skin irritation, seizure in children (topical near face) |
| False Unicorn Root | Chamaelirium luteum | Avoid during pregnancy except under qualified supervision. Use caution with hormone-sensitive conditions. At-risk plant species; use sustainably sourced supply only. | Nausea, vomiting in high doses, hormonal disruption |
| Fennel | Foeniculum vulgare | Avoid medicinal doses during pregnancy. Use caution with estrogen-sensitive conditions. | Allergic reaction, skin sensitivity to sunlight, hormonal effects |
| Feverfew | Tanacetum parthenium | Avoid during pregnancy (uterine stimulant). Do not stop abruptly after long-term use. Avoid with blood thinners. | Post-use rebound headaches, mouth ulcers, GI upset, increased bleeding risk |
| Figwort | Scrophularia nodosa | Avoid with heart conditions and cardiac medications. Avoid during pregnancy. Use only under qualified supervision. | Heart palpitations, GI upset, possible cardiac stimulation |
| Garlic | Allium sativum | Avoid high doses before surgery. Use caution with blood thinners and HIV medications. | Bad breath, GI upset, heartburn, increased bleeding risk |
| Gentian | Gentiana lutea | Avoid with stomach ulcers, gastritis, and high blood pressure. Avoid during pregnancy. | Headache, nausea, GI irritation, elevated blood pressure |
| Ginger | Zingiber officinale | Use caution with blood thinners and diabetes medications. High doses may cause issues in late pregnancy. | Heartburn, mouth irritation, diarrhea, blood-thinning effect |
| Ginkgo | Ginkgo biloba | Avoid with blood thinners, antidepressants, and before surgery. Not for children. | Headache, dizziness, GI upset, increased bleeding risk |
| Ginseng (American) | Panax quinquefolius | Avoid with stimulants, blood thinners, and diabetes medications. Limit continuous use. | Insomnia, headache, GI upset, blood pressure changes |
| Ginseng (Asian) | Panax ginseng | Avoid with stimulants, blood thinners, and MAOIs. Not recommended for long-term uninterrupted use. | Insomnia, nervousness, elevated blood pressure, headache |
| Goldenseal | Hydrastis canadensis | Avoid during pregnancy and with blood pressure medications. Do not use long-term. | Nausea, digestive irritation, elevated blood pressure, liver stress |
| Goldenrod | Solidago virgaurea | Avoid with kidney disease, edema from heart or kidney failure, and ragweed allergy. Use caution with diuretics. | Allergic reaction, increased urination, GI upset |
| Guggul | Commiphora wightii | Avoid with thyroid medications, estrogen therapies, and blood thinners. Use caution with liver conditions. | Nausea, GI upset, skin rash, thyroid hormone interference, headache |
| Hawthorn | Crataegus monogyna | Use caution with heart medications and digoxin. Consult a physician if treating cardiac conditions. | Dizziness, nausea, fatigue, headache, palpitations |
| He Shou Wu (Fo-Ti) | Polygonum multiflorum | Avoid with liver conditions and hepatotoxic medications. Do not use long-term without supervision. Processed and raw forms differ significantly in safety. | Liver damage, hepatotoxicity, diarrhea, skin rash, numbness |
| Holy Basil (Tulsi) | Ocimum tenuiflorum | Avoid with blood thinners and diabetes medications. Use caution during pregnancy. | Low blood sugar, blood-thinning effect, drowsiness |
| Hops | Humulus lupulus | Avoid with sedatives and alcohol. Not recommended for depression. | Drowsiness, dizziness, hormonal effects |
| Horse Chestnut | Aesculus hippocastanum | Raw seeds, leaves, and bark are toxic. Use only standardized extract (escin). Avoid with blood thinners, kidney disease, and liver disease. | Nausea, GI upset, dizziness, itching; raw plant causes severe toxicity |
| Horsetail | Equisetum arvense | Avoid during pregnancy and with diuretics, heart medications, and nicotine patches. Do not use long-term. Contains thiaminase; may deplete vitamin B1. | Thiamine deficiency, electrolyte imbalance, GI upset, kidney irritation |
| Kava / Kava-Kava | Piper methysticum | Avoid with alcohol, sedatives, and liver-affecting medications. Do not use daily long-term. | Liver damage, drowsiness, skin discoloration with heavy use |
| Kelp | Laminaria spp. | Avoid with thyroid disorders and iodine sensitivity. Do not use during pregnancy or with thyroid medications. Source carefully to avoid heavy metal contamination. | Thyroid disruption, iodine toxicity, heavy metal accumulation, acne |
| Lavender | Lavandula angustifolia | Avoid oral use with sedatives. Topical use is generally safe. Avoid undiluted essential oil on skin. | Drowsiness, skin irritation, hormonal disruption (topical in children) |
| Lemon Balm | Melissa officinalis | Use caution with thyroid medications and sedatives. | Drowsiness, nausea, dizziness, thyroid interference |
| Licorice Root | Glycyrrhiza glabra | Avoid with high blood pressure, kidney disease, heart conditions, and corticosteroids. Limit use to under 4 weeks. | Elevated blood pressure, fluid retention, low potassium, hormonal effects |
| Lobelia | Lobelia inflata | Extremely narrow safety margin. Avoid during pregnancy, with heart conditions, high blood pressure, and tobacco use. Use only under qualified supervision. | Nausea, vomiting, diarrhea, tremors, rapid heart rate, respiratory depression, death in overdose |
| Marshmallow Root | Althaea officinalis | May slow absorption of oral medications; take separately. Use caution with diabetes medications. | Low blood sugar, possible delayed drug absorption |
| Milk Thistle | Silybum marianum | Generally safe. Use caution with estrogen-sensitive conditions and diabetes medications. | Mild laxative effect, allergic reaction (ragweed family), GI upset |
| Motherwort | Leonurus cardiaca | Avoid during pregnancy and with heart medications or sedatives. | Drowsiness, uterine stimulation, skin photosensitivity |
| Mullein | Verbascum thapsus | Generally considered safe. Strain tea well to remove fine hairs that can irritate the throat. | Rare contact dermatitis, throat irritation if not strained |
| Myrrh | Commiphora myrrha | Avoid during pregnancy (uterine stimulant). Use caution with diabetes medications and blood thinners. Avoid with kidney conditions. | GI upset, diarrhea, skin rash, uterine stimulation, kidney irritation in high doses |
| Nettle | Urtica dioica | Use caution with blood thinners, diuretics, and diabetes medications. | Fluid retention changes, GI upset, allergic reaction, low blood sugar |
| Oatstraw | Avena sativa | Generally considered safe. Avoid with gluten sensitivity or celiac disease (cross-contamination risk). Use caution with sedatives. | Mild drowsiness, GI discomfort, gluten reaction in sensitive individuals |
| Parsley | Petroselinum crispum | Culinary amounts are safe. Avoid medicinal or seed oil doses during pregnancy (uterine stimulant). Use caution with diuretics and anticoagulants. | Uterine stimulation, photosensitivity, kidney irritation in high doses, increased bleeding risk |
| Passionflower | Passiflora incarnata | Avoid during pregnancy and with sedatives or MAOIs. | Drowsiness, dizziness, confusion, rapid heartbeat (high doses) |
| Peppermint | Mentha piperita | Avoid with acid reflux (may worsen). Do not apply menthol near infants’ faces. Use caution with cyclosporine. | Heartburn, allergic reaction, headache, skin irritation |
| Poke Root | Phytolacca americana | Highly toxic plant. Internal use is extremely dangerous and not recommended. Topical use requires great caution. Avoid during pregnancy. Use only under qualified expert supervision. | Severe nausea, vomiting, diarrhea, respiratory depression, cardiac arrest, death in overdose |
| Red Clover | Trifolium pratense | Avoid with hormone-sensitive cancers, blood thinners, and hormone therapies. | Headache, nausea, rash, hormonal effects |
| Reishi Mushroom | Ganoderma lucidum | Use caution with blood thinners, immunosuppressants, and blood pressure medications. Avoid before surgery. | Dry mouth, dizziness, GI upset, nosebleed, liver toxicity with prolonged high-dose use |
| Rosemary | Salvia rosmarinus | Culinary use is safe. Avoid medicinal doses during pregnancy. Use caution with blood thinners and ACE inhibitors. | Seizures at very high doses, GI upset, skin irritation |
| Sage | Salvia officinalis | Avoid medicinal doses during pregnancy and with seizure disorders. Limit long-term high-dose use. | Dry mouth, dizziness, rapid heartbeat, seizure risk (thujone content) |
| Sarsaparilla | Smilax ornata | Avoid with kidney disease and with medications requiring careful dosing (may alter absorption). Use caution with diuretics. | GI upset, increased urination, kidney irritation, altered drug absorption |
| Shepherd’s Purse | Capsella bursa-pastoris | Avoid during pregnancy and with thyroid conditions. Use caution with blood pressure and heart medications. | Uterine stimulation, thyroid disruption, sedation, heart palpitations |
| St. John’s Wort | Hypericum perforatum | Interacts with many medications including antidepressants, birth control, and blood thinners. Avoid with photosensitive skin. | Photosensitivity, serotonin syndrome risk, GI upset, fatigue |
| Turmeric | Curcuma longa | Avoid high doses with blood thinners, diabetes medications, and before surgery. | GI upset, nausea, diarrhea, increased bleeding risk in high doses |
| Uva-Ursi (Bearberry) | Arctostaphylos uva-ursi | Avoid during pregnancy and breastfeeding. Do not use more than 5 days continuously. Avoid with kidney disease and acidic foods or supplements. Requires alkaline urine to activate. | Nausea, vomiting, liver toxicity with prolonged use, greenish-brown urine discoloration |
| Valerian | Valeriana officinalis | Avoid with sedatives, alcohol, and anesthesia. Do not drive after use. | Drowsiness, vivid dreams, headache, liver stress (rare, long-term) |
| Willow Bark | Salix alba | Avoid with aspirin sensitivity, blood thinners, NSAIDs, and in children under 16 (Reye’s syndrome risk). Avoid with kidney or liver disease. | GI upset, stomach ulcers, increased bleeding risk, Reye’s syndrome in children |
| Yarrow | Achillea millefolium | Avoid during pregnancy. Use caution with blood thinners and sedatives. Avoid with ragweed allergy. | Allergic skin reaction, photosensitivity, drowsiness |
| Yellow Dock | Rumex crispus | Avoid with kidney stones, kidney disease, and gout. Use caution with blood thinners and calcium-affecting medications. Do not use long-term. | Diarrhea, nausea, kidney stone formation, electrolyte imbalance, skin irritation |
The herbal world is vast, ancient, and deeply powerful. Used wisely, herbs can support wellness, complement nutrition, and enrich daily life in meaningful ways. Used carelessly, they can cause real harm. This guide is a starting point, not a substitute for professional medical advice. Always research each herb thoroughly before use, disclose all herbal supplements to your healthcare provider, and pay close attention to how your body responds. Be especially cautious when managing chronic conditions, taking prescription medications, or caring for vulnerable individuals such as the elderly or those with disabilities. Quality sourcing, proper dosing, and informed intention are the foundations of safe herbal practice. Let knowledge, not assumption, guide your relationship with plants.
“What I like about herbs is that they span the spectrum between food and medicine. Herbs enhance our food when we are hungry, nourish our bodies when we are depleted, and provide pharmacological interventions when we are ill. Herbs are generally less specific and more supportive than drugs.”
– Adriane Fugh-Berman M.D, medicinal officer at National Institute of Health
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