Herb-Drug Interactions: What the Science Says

Cat's Claw

Indigenous people of the Amazon rainforest have used cat’s claw for centuries to ward off disease. Today, cat’s claw is promoted for osteoarthritis, rheumatoid arthritis, cancer, viral infections, and other conditions.

Potential for Herb-Drug Interactions

• Cat’s claw may interact with anticoagulant/antiplatelet drugs, antihypertensive drugs, calcium channel blockers, cytochrome P450 3A4 (CYP3A4) substrates, and immunosuppressants.

Efficacy

• There’s no conclusive scientific evidence based on studies in people that supports using cat’s claw for any health purpose, including COVID-19. Some research has been done in people on the effect of cat’s claw on various conditions, but many of the studies did not use rigorous methods and did not include enough study participants to allow definite conclusions to be reached.

Safety

• Cat’s claw appears to be safe when used orally for short periods of time, as much as 6 months. However, there is insufficient reliable information about its safety when applied to the skin. Cat’s claw might make the immune system more active, which could increase symptoms of autoimmune diseases. 
• Cat’s claw may slow blood clotting, and this might increase the risk of bleeding during surgery.
• There are theoretical reasons to suspect that cat’s claw might interact with anticoagulant, antiplatelet, and antihypertensive drugs, and other supplements as well. 
• Some studies of the use of cat’s claw during pregnancy suggest it is unsafe. Little is known about whether it’s safe to use cat’s claw while breastfeeding.

Chamomile

Chamomile is promoted for the common cold, indigestion, anxiety, insomnia, colic in infants, respiratory disorders such as cough and bronchitis, and many other conditions. It is also used topically for some skin conditions and as a mouthwash.

Potential for Herb-Drug Interactions

• Preliminary studies suggest that taking chamomile along with oral contraceptives might decrease the effects of oral contraceptives. 
• Interactions between chamomile and some drugs metabolized by the liver and warfarin have been reported, and there are theoretical reasons to suspect that chamomile might interact with other drugs as well, such as sedatives.

Efficacy

• Some preliminary studies suggest that a chamomile dietary supplement might be helpful for generalized anxiety disorder and associated depression.
• Some research has found that products containing certain combinations of herbs that include chamomile may be of benefit for diarrhea in children and for infants with colic. But chamomile alone has not been shown to be helpful for these conditions.
• Small studies suggest that mouthwashes containing chamomile might prevent or treat swelling or irritation in the mouth resulting from radiation therapy, chemotherapy, or stem cell transplantation.
• There’s very little information on chamomile’s effect on insomnia. A 2019 review of chamomile use found one study on insomnia, which found no benefit from its use for this sleep disorder.

Safety

• Chamomile is likely safe when used orally in amounts commonly found in teas and other foods. It is possibly safe when used by adults and children orally for medicinal purposes over the short term. Using chamomile on the skin in adults and children or as an oral rinse for medicinal purposes is possibly safe at certain doses and over the short term. 
• Side effects are uncommon and may include nausea, dizziness, and allergic reactions, including severe hypersensitivity reactions and anaphylaxis, in some people. If used near the eyes, chamomile might cause eye irritation.
• People are more likely to experience allergic reactions to chamomile if they’re allergic to related plants such as ragweed, chrysanthemums, marigolds, or daisies.
• Chamomile might have some of the same effects as estrogen. Preliminary studies suggest that taking chamomile along with oral contraceptives might decrease the effects of oral contraceptives. In addition, chamomile might worsen any condition that is sensitive to exposure to estrogen, such as breast or uterine cancer.
• Interactions between chamomile and some drugs metabolized by the liver and warfarin have been reported, and there are theoretical reasons to suspect that chamomile might interact with other drugs as well, such as sedatives. 
• Little is known about whether it’s safe to use chamomile during pregnancy or while breastfeeding.

Cranberry

Cranberry is commonly promoted for urinary tract infections (UTIs) and recurrent UTIs. Cranberry products are promoted for these common infections in part because of a growing interest in nonantibiotic prevention strategies, given concerns about antibiotic-resistant bacteria.

Potential for Herb-Drug Interactions

There is conflicting evidence about whether cranberry interacts with the anticoagulant warfarin.

Efficacy

• In general, cranberry products may decrease the overall risk of symptomatic, recurrent UTIs in women by 25 percent, and in some cases, by more than 30 percent. However, the effectiveness of cranberry is still in question because of inconsistent findings.
• While cranberry may assist in preventing symptomatic UTIs in some women, it isn’t recommended as a treatment for existing UTIs in any population.
• It’s thought that the proanthocyanidins (PACs) present in cranberries prevent bacteria from sticking to the bladder wall, thus preventing the start of a UTI. Processing cranberries into various products, like tablets or capsules, can reduce the concentration of PACs, which can reduce the potential effectiveness of a product.
• Studies in certain populations at increased risk for UTIs, such as elderly people in long-term care and pregnant women, have had inconsistent results. Studies in other high-risk populations, such as women undergoing gynecological surgeries or people with multiple sclerosis, have not found cranberry to be beneficial in reducing the risk for UTIs.
• Starting in 2020, the U.S. Food and Drug Administration has allowed manufacturers to claim on product labels that there is “limited” evidence that daily consumption of specified amounts of cranberry dietary supplements may reduce the risk of recurrent UTIs in healthy women. A similar claim may be made for cranberry juice beverages, but the evidence must be described as “limited and inconsistent.”

Safety

• Cranberry taken orally is generally thought to be safe. However, if consumed in very large amounts, cranberry can cause stomach upset and diarrhea, particularly in young children.
• There is conflicting evidence about whether cranberry interacts with the anticoagulant warfarin. 
• Some studies of the use of cranberry during pregnancy or while breastfeeding suggest it is safe in amounts commonly found in food, but the evidence is not conclusive for use in larger amounts.

Ginkgo

Ginkgo leaf, usually as an extract, is the most commonly used form of ginkgo. Ginkgo is promoted as a dietary supplement for many conditions, including anxiety, heart disease, cognitive impairment and dementia, diabetes, premenstrual syndrome (PMS), schizophrenia, and tinnitus, among others. It has also been promoted with claims that it can enhance cognitive performance in healthy people.

Potential for Herb-Drug Interactions

Taking Ginkgo biloba with warfarin is associated with increased risk for major bleeding events compared to warfarin alone. Concomitant use of Ginkgo biloba preparations and efavirenz (a non-nucleoside reverse transcriptase inhibitor) is not recommended.

Efficacy

• There’s no conclusive evidence that ginkgo is helpful for any health condition. 
• Ginkgo extract may have a modest benefit for dementia symptoms, particularly at relatively high doses, but the evidence is inconsistent. Ginkgo has not been shown to be beneficial for preventing or slowing the progression of dementia. It’s unclear whether ginkgo is helpful for symptoms of milder cognitive impairment. 
• Although dietary supplements containing ginkgo have been marketed for “brain health,” it’s uncertain whether they influence cognitive performance in healthy people. Much of the research on this topic is of low quality. 
• For various health conditions, including anxiety, PMS, schizophrenia, and vertigo, a small amount of evidence suggests a benefit from taking ginkgo orally, but the overall evidence is not conclusive. Ginkgo might also be helpful in the rehabilitation of patients who have had strokes. 
• Research suggests that ginkgo is not helpful for preventing heart disease, treating high blood pressure, or relieving symptoms of tinnitus or multiple sclerosis. 

Safety

• For most adults, ginkgo leaf extracts are likely to be safe when taken orally in moderate amounts. They have been used safely in research studies lasting as long as 6 years. Fresh ginkgo seeds are toxic when consumed orally, and serious side effects have also occurred in people who consumed roasted ginkgo seeds or the crude ginkgo plant. 
• Ginkgo leaf extract is generally well tolerated; the most common side effects are dizziness, gastrointestinal symptoms, and headache. 
• Ginkgo may increase the risk of bleeding in people who are taking anticoagulant drugs, such as warfarin. Ginkgo may also interact with other drugs. 
• Ginkgo may be unsafe for use during pregnancy. It might cause early labor or extra bleeding during delivery if used near that time. Little is known about whether it’s safe to use ginkgo while breastfeeding.

Goldenseal

Goldenseal is promoted as a dietary supplement for colds and other respiratory tract infections, allergic rhinitis, ulcers, and digestive upsets such as diarrhea and constipation. It is also used as a mouthwash for sore gums and as an eyewash for eye inflammation, and it is applied to the skin for rashes and other skin problems.

Potential for Herb-Drug Interactions

• A 2021 study found that levels of metformin decreased about 25 percent in healthy adults who were given goldenseal extract plus metformin. This drop was enough to potentially hinder glucose control in people with type 2 diabetes taking metformin.
• A 2017 review found goldenseal to have an overall high risk of drug interactions because it has been shown to inhibit two major metabolic enzymes, CYP2D6 and CYP3A4, which are responsible for metabolism of more than half of currently used pharmaceutical agents.

Efficacy

• The scientific evidence does not support the use of goldenseal for any health-related purpose.
• Berberine, a substance found in goldenseal, has been studied for heart failure, diarrhea, infections, and other health conditions. However, when people take goldenseal orally, very little berberine may be absorbed by the body or enter the bloodstream, so study results on berberine may not apply to goldenseal.

Safety

• Little information is available on the safety of goldenseal taken alone. Goldenseal might be safe for most adults when taken by mouth in the short term. There is not enough reliable information to know if goldenseal is safe for long-term use.
• Goldenseal should not be used when pregnant or breastfeeding, and it should not be given to infants. Berberine can cause or worsen jaundice in newborn infants and could lead to a life-threatening problem called kernicterus.
• A study funded by the National Center for Complementary and Integrative Health (NCCIH) found that some commercial goldenseal dietary supplements didn’t contain much goldenseal and instead included ingredients not listed on their labels.

Green Tea

Green tea and its extracts are often promoted as dietary supplements for losing weight, reducing blood cholesterol levels, and preventing chronic diseases such as heart disease and cancer.  Some products marketed for weight loss contain green tea in combination with other ingredients. 

The U.S. Food and Drug Administration (FDA) has approved a topical ointment containing a specific green tea extract for the treatment of external genital and perianal warts.

Potential Herb-Drug Interactions

Green tea at high doses has been shown to reduce blood levels and, therefore, the effectiveness of the drug nadolol, a beta-blocker used for high blood pressure and heart problems. Green tea extract can reduce blood levels of the cholesterol-lowering drug atorvastatin. Green tea may also interact with other medicines.

Efficacy

• The FDA has approved a specific green tea extract ointment as a prescription drug for treating genital warts. 
• Many studies have looked at the relationship between green tea consumption and the risk of various types of cancer. The overall results of these studies have been inconsistent. 
• In Asian populations but not in Western populations, green tea consumption has been linked to a lower risk of coronary heart disease. 
• The catechins and caffeine in green tea and its extracts may have a modest effect on body weight. However, the effects of green tea products may vary depending on the composition of the product and the individual’s level of physical activity. 
• The effect of green tea on blood cholesterol levels has been tested in studies in which people were randomly assigned to consume either a green tea product or a placebo. Most of the studies evaluated green tea extract supplements rather than green tea as a beverage. Green tea reduced total cholesterol and low-density lipoprotein (LDL) cholesterol to a small extent, but it did not affect high-density lipoprotein (HDL) cholesterol or triglycerides. 

Safety

• Side effects of green tea extract supplements include nausea, constipation, abdominal discomfort, and increased blood pressure. 
• Although uncommon, liver injury has been reported in some people who used green tea products, primarily green tea extracts in tablet or capsule form. Individuals with a specific variant of a gene that plays an important role in immune function appear to be especially susceptible. Between 5 and 15 percent of Americans have this variant. 
• Green tea at high doses has been shown to reduce blood levels and, therefore, the effectiveness of the drug nadolol, a beta-blocker used for high blood pressure and heart problems. Green tea extract can reduce blood levels of the cholesterol-lowering drug atorvastatin. Green tea may also interact with other medicines. 
• During pregnancy, caffeine intake should not exceed moderate levels. Green tea is a source of caffeine. Breastfeeding infants usually do not have adverse effects when mothers consume low-to-moderate levels of caffeine. 

St. John's Wort

St. John’s wort is promoted for depression, menopausal symptoms, attention-deficit hyperactivity disorder (ADHD), somatic symptom disorder, obsessive-compulsive disorder, and other conditions. Topical use of St. John’s wort is promoted for various skin conditions, including wounds, bruises, and muscle pain.

Potential for Herb-Drug Interactions

• St. John’s wort has an overall high risk of drug interaction because it is a potent inducer of both cytochrome P-450 enzymes and intestinal P-glycoprotein.
• Clinically significant interactions between St. John’s wort and the immunosuppressant drug cyclosporine, the antiretroviral agent indinavir, oral contraceptives, warfarin, digoxin, and benzodiazepines, among others, have been documented.
• Taking St. John’s wort with certain antidepressants may lead to increased serotonin-related side effects, which may be potentially serious.

Efficacy

• A 2009 Cochrane systematic review of 29 international studies suggested that St. John’s wort may be better than a placebo and as effective as standard prescription antidepressants for major depression of mild to moderate severity. It’s uncertain whether this is true for severe depression and for time periods longer than 12 weeks. St. John’s wort also appeared to have fewer side effects than standard antidepressants. The studies conducted in German-speaking countries—where St. John’s wort has a long history of use by medical professionals—reported more positive results than those done in other countries, including the United States. 
• St. John’s wort has also been studied for conditions other than depression. For some, such as irritable bowel syndrome, chronic hepatitis C virus infection, HIV infection, and social anxiety disorder, current evidence suggests that St. John’s wort isn’t helpful.
• St. John’s wort might be helpful for menopausal symptoms, wound healing, and somatic symptom disorder, but there’s not enough evidence to know for certain.
• There’s not enough reliable evidence to know whether St. John’s wort might be beneficial for quitting smoking or improving memory or for many conditions, including anxiety, ADHD, and seasonal affective disorder.

Safety

• St. John’s wort may cause increased sensitivity to sunlight, especially when taken in large doses. Other side effects can include insomnia, anxiety, dry mouth, dizziness, gastrointestinal symptoms, fatigue, headache, or sexual dysfunction.
• Taking St. John’s wort with certain antidepressants may lead to increased serotonin-related side effects, which may be potentially serious.
• There isn’t enough reliable information available to know if St. John’s wort is safe when used topically. It may cause severe skin reactions to sun exposure.
• It may not be safe to use St. John’s wort during pregnancy or while breastfeeding. It has caused birth defects in laboratory animals. Infants breastfed by mothers who take St. John’s wort can experience colic, drowsiness, and fussiness.

References