Herbs & Supplements

What interactions should I watch for?

Prescription Drugs

In studies, St. John's wort has been shown to increase elimination of the anticoagulant drug, warfarin, from the body. As a result, less warfarin may be available, blood clotting may not be controlled adequately, and blood clots may form. Whether St. Johns wort interferes with the effects of other anticoagulants or similar drugs known as antiplatelets is not yet known. Individuals who take an anticoagulant or an antiplatelet drug should check with a doctor or pharmacist before beginning to take St. John's wort, too.

• Antiplatelets include clopidogrel and Ticlid
• Anticoagulants include heparin and warfarin

In some cases, when St. John's wort was taken at the same time as certain prescription antidepressants, more side effects were experienced. These side effects included fatigue, nausea, restlessness, sweating, and vomiting. Among the drugs involved were:

• Monoamine oxidase inhibitors such as Marplan, Nardil, and tranylcypromine (Parnate)
• nefazodone
• Selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine, paroxetine, and sertraline
• Tricyclic antidepressants such as amitriptyline and nortriptyline

Because it is broken down by certain enzymes in the liver, St. John's wort may possibly interfere with the use of prescription drugs that are processed by the same enzymes. Some of these drugs are:

• Allergy drugs such as fexofenadine
• Antifungal drugs such as itraconazole and ketoconazole
• Cancer drugs such as Camptosar, etoposide, Gleevec, paclitaxel (Taxol), vinblastine, or vincristine
• Certain calcium channel blockers such as diltiazem and nifedipine

St. John's wort is believed to affect the amounts of a body chemical known as P-glycoprotein, which serves as a carrier for many types of drugs, including digoxin. When St. John's wort and digoxin are taken together, the blood levels of digoxin may decrease significantly and the control of heart conditions treated by digoxin may not be maintained. St. John's wort should not be taken with digoxin.

By altering enzyme activity, St. John's wort appears to lower blood levels of at least two classes of drugs that are used to treat HIV and AIDS. St. John's wort should be avoided by individuals who take non-nucleoside reverse transcriptase inhibitors such as delavirdine (Rescriptor) and nevirapine (Viramune) and protease inhibitors such as indinavir (Crixivan), ritonavir (Norvir), and nelfinavir (Viracept). The effects of St. John's wort on other classes of drugs used to treat HIV-related conditions is not known, but individuals who are taking any anti-HIV drugs may want to avoid taking St. John's wort.

St. John's wort may activate enzymes that break down certain drugs; therefore, it may interfere with the effects of drugs used to suppress the immune system after organ transplants or in other conditions. Taking St. John's wort is not recommended for patients who take drugs such as:

• azathioprine (Imuran)
• CellCept
• cyclosporine (Neoral, Sandimmune)
• Prograf
• Rapamune
• Zenapax

St. John's wort may interfere with the body's use of oral contraceptives. Irregular vaginal bleeding may result and contraceptives may not be as effective. To prevent unplanned pregnancy, women who take St. John's wort should use an additional form of birth control different from oral contraceptives.

In small studies of healthy individuals, St. John's wort reduced the the effectiveness of the anti-cholesterol drugs, atorvastatin (Lipitor) and simvastatin (Zocor). Levels of a similar drug, pravastatin (Pravachol), were not changed. Other drugs in the class known as statins (Crestor, Lescol, and lovastatin) may be affected by St. John's wort. Therefore, individuals using one of the statin drugs to reduce cholesterol should not start taking St. John's wort until a doctor or pharmacist determines the potential for an interaction.

In a recent study, taking St. John's wort reduced the amounts of omeprazole (Prilosec) in the blood. As a result, the effects of omeprazole were much less than expected. Omeprazole belongs to a class of drugs known as proton pump inhibitors, which is used to treat ulcers and other gastrointestinal (GI) conditions.

Drugs known as psoralens cause the skin to be excessively sensitive to sunlight. Psoralens include Oxsoralen (methoxsalen or 8-MOP). In addition, some antibiotics such as ciprofloxacin and tetracycline may make the skin more likely to sunburn. If St. John's wort, which also sensitizes the skin to light, is taken at the same time as another of these sun-sensitizing drugs, the chance of sunburn increases.

For unknown reasons, St. John's wort blocks the effects of a heart drug known as reserpine. The two products should not be taken together.

When St. John's wort is used with prescription drugs that promote sleepiness, the effects of the drug may be exaggerated, resulting in sedation or mental impairment. Prescription drugs that can cause sleepiness include:

• Anticonvulsants such as carbamazepine, divalproex sodium, phenytoin, and valproic acid
• Barbiturates such as phenobarbital
• Benzodiazepines such as alprazolam and diazepam
• Drugs for insomnia such as Lunesta, Rozerem, zaleplon, and zolpidem
• Tricyclic antidepressants such as amitriptyline, amoxapine, doxepin, and nortriptyline

Through a process that is not understood completely, St. John's wort may decrease both the blood levels and the effectiveness of theophylline, a drug used to treat asthma and other breathing conditions. If the two are taken together, breathing may not be controlled adequately and asthma attacks may be more likely to occur. Theophylline has numerous brand names such as Aerolate, T-Phyl, and Uniphyl. Individuals who take an oral medication for asthma should check with a doctor or pharmacist before beginning to take St. John's wort.

If St. John's wort is taken at the same time as one of the drugs that belongs to a class known as triptans, the risk of side effects--including serotonin syndrome--may go up. Triptans are usually taken to relieve the pain of migraine headaches. They include:

• Amerge
• Axert
• Frova
• Imitrex
• Zomig

Non-prescription Drugs

Dextromethorphan (DM) is an anti-coughing ingredient in many non-prescription cough and cold products such as Nyquil and Robitussin DM. Because it may have an increasing effect on serotonin levels, taking DM with St. John's wort may result in a higher risk of side effects.

Because the tannins in St. John's wort may block the absorption of iron by the body, iron-deficiency anemia is possible. Symptoms of iron-deficiency anemia may include dizziness, fatigue, low blood pressure, and cold, pale skin.

The sleep-producing effects of over-the-counter products containing diphenhydramine or doxylamine can be enhanced by taking St. John's wort at the same time. Diphenhydramine and doxylamine are contained in many non-prescription sleeping pills as well as in some cough and cold products, therefore caution should be used when taking these medications with St. John's wort because excessive drowsiness may result.

Herbal Products

St. John's wort may cause excessive sedation if it is taken with other potentially sedating herbs such as:

• Catnip
• Hops
• Kava
• Valerian

Foods

No interactions between St. John's wort and foods have been reported, but drinking alcohol at the same time as using St. John's wort by mouth may result in increased drowsiness.

Some interactions between herbal products and medications can be more severe than others. The best way for you to avoid harmful interactions is to tell your doctor and/or pharmacist what medications you are currently taking, including any over-the-counter products, vitamins, and herbals. For specific information on how St, John's wort interacts with drugs, other herbals, and foods and the severity of those interactions, please use our Drug Interactions Checker to check for possible interactions.