Dangerous Drug Interactions with Herbal Medicine St. John's Wort

As a pharmacist, I know that people forget to tell doctors and pharmacists about all prescription and over-the-counter medications they are taking, especially herbal medicines. This is critical so that drug interaction problems can be avoided. St. John's Wort, an over-the-counter herbal medicine for depression, exhibits at least 70 drug interactions that have major clinical significance. There are also more than 450 drug interactions between this herbal medicine and other drugs that are of moderate clinical significance.

St. John's Wort Decreases Effectiveness of Other Drugs

St. John's Wort causes some drug levels to be decreased by inducing liver enzymes (cytochrome P450 3A4 enzyme system) and by affecting how substances are transported across cell membranes (permeability glycoprotein).

A Harvard Medical School study concluded that taking this herbal medicine concurrently with some medications causes them to be only half as effective.

Drug interactions between St. John's Wort and oral contraceptives have resulted in unexpected bleeding and unintentional pregnancies.

Transplant patients taking this herbal medicine have experienced a drop in blood levels of cyclosporine and rejection of transplants.

The drop in digoxin levels due to the drug interaction with this herbal medicine can be very serious for congestive heart failure patients and patients with arrhythmias.

Warfarin drug interactions with St. John's Wort can be very dangerous, decreasing warfarin blood levels and interfering with its ability to prevent blood clots.

Blood levels and effectiveness of the cholesterol-lowering drug, simvastatin, are decreased due to a drug interaction with St. John's Wort.

St. John's Wort interacts with indinavir, an antiretroviral used to treat HIV, to decrease its blood levels between 49 and 99%.

The anti-cancer effects of irinotecan are severely reduced by several mechanisms when taken with St. John's Wort.

Additive Central Nervous System Effects with this Herbal Medicine

Antidepressants such as St. John's Wort can increase drowsiness and respiratory depression caused by pain relievers such as propoxyphene. This drug interaction can also occur when St. John's Wort is taken with antidepressants, anti-anxiety medications, and many other medications that act on the central nervous system .

Serotonin Syndrome Drug Interactions

Using St. John's Wort together with drugs such as amitriptyline, dextromethorphan, and many other drugs like monoamine oxidase inhibitors, can cause a rare but possibly fatal reaction called serotonin syndrome. This syndrome can cause mental changes including irritability, confusion, hallucinations, and coma. Rapid heart rate, high temperature, sweating, fluctuation in blood pressure, and dilated pupils can occur. Tremor, muscle rigidity, exaggerated reflexes, and staggering are possible as well as gastrointestinal symptoms such as nausea, vomiting, cramping, and diarrhea.

Summary

Drug interactions with St. John's Wort can intensify side effects of other drugs, causing dangerous respiratory depression. Drug interactions with this herbal medicine can cause life-threatening serotonin syndrome. Drug interactions with St. John's Wort can also cause many life-saving drugs to lose their effectiveness by decreasing their blood levels. The drug-interactions listed above are only a few of the possible problems with St. John's Wort and other drugs when taken together. This brief discussion of drug interactions with St. John's Wort points to the importance of telling your doctor and pharmacist about all herbal medicine and all other medicines you are taking.

Sources:

L. Henderson, Q Y Yue, C. Berquist, B. Gerden, P. Arlett. St John's wort (Hypericum perforatum): Drug interactions and clinical outcomes. National Center for Biotechnology Information, U. S. National Library of Medicine.

R. Madabushi, B. Frank, B. Drewelow, H. Derendorf, V. Butterweck. Hyperforin in St. John's Wort drug interactions. National Center for Biotechnology Information, U. S. National Library of Medicine.

No author given. St. John's Wort Drug Interactions. The Harvard Medical School.

M. Mannel. Drug interactions with St John's Wort : mechanisms and clinical implications. National Center for Biotechnology Information, U. S. National Library of Medicine.

No author given. Drug Interaction Checker. Medscape.

No author given. Drug Interactions Checker. Drugs.com.

No author given. Herbal Medicine. MedlinePlus.

L. G. Miller. Traditional Herbal Medicines in Modern Research and Clinical Trials. Floraleads.