In other words, a drug interaction can be dangerous because it increases harmful side effects and possibly creates a toxic level of a drug in the body. Or, a drug interaction may lead to reduced relief of symptoms, even increasing the risk of serious health problems such as heart attack or organ rejection. For example, taking a sedative with an antihistamine can slow your reactions and make driving dangerous. Simply drinking grapefruit juice can interfere with the metabolism of medications such as calcium channel-blockers. The juice uses the enzyme that normally breaks down the drug, Wattigny explains, so more of the drug stays in the body longer, increasing its effect.
Herbal preparations can also cause harmful drug interactions.
For example, the Food and Drug Administration now advises that St. John's wort may interfere with drugs used to treat conditions such as heart disease, seizures and certain cancers. The herb may also reduce the effectiveness of oral contraceptives and drugs used to prevent transplant rejection. Problems can arise when a patient sees multiple doctors or goes to more than one pharmacy. Although every doctor or pharmacist you see should know all the drugs you're taking, it can help to centralize your medication management. If you see one or more specialists, keep your primary care physician informed about your treatment plans.