Many Americans take both dietary supplements and prescription or over-the-counter drugs. Sometimes, these drugs and supplements may interact in harmful ways. 

Talk with your healthcare providers or Care Team 

It’s important to tell all your healthcare providers about all dietary supplements and drugs you take. That way, they can help you avoid harmful interactions. 

Often, when you visit a healthcare provider for the first time, you fill out a form that asks you to list all the drugs and supplements you take. Be sure to update this information every time you visit the provider’s office. 

Some supplements may increase the effects (and side effects) of drugs 

Sometimes, taking a drug and a supplement together may increase the drug’s effects. The drug’s effects may become too strong, and unwanted side effects may increase. 

For example, the herbs Schisandra and goldenseal may slow down the processes in your body that change drugs into inactive substances. So, if you take these herbs while you’re also taking a drug, the amount of the drug in your body may increase. As a result, the drug’s effects may be too strong. 

Some supplements may decrease the effects of drugs 

Sometimes, taking a drug and a supplement together may decrease the drug’s effects. This means that you aren’t getting the full benefit from the drug that your healthcare provider wants you to have. 

One popular herbal supplement, St. John’s wort, is especially well known for decreasing the effects of drugs. It does this by speeding up the processes in your body that change drugs into inactive substances. This herb may decrease the effectiveness of more than 70 percent of all drugs. 

Some drugs that interact with St. John’s Wort  

• Anesthetics  
• Anti-anxiety drugs 
• Anticoagulants (blood thinners) 
• Antidepressants  
• Cancer drugs  
• Cholesterol-lowering drugs (statins)  
• Diabetes drugs 
• Digoxin (digitalis), a drug used to treat heart problems 
• Drugs that suppress the immune system (used to prevent rejection of transplanted organs) 
• Drugs used to prevent seizures 
• Drugs used to treat HIV infection 
• Fexofenadine (an antihistamine) 
• Finasteride (a drug used for prostate problems) 
• Ivabradine (a drug used to treat angina) 
• Methadone  
• Nifedipine and verapamil (used to treat high blood pressure or heart problems) 
• Omeprazole (an acid reducer used to treat digestive tract problems)  
• Oral contraceptives (birth control pills)  
• Talinolol (a beta-blocker used for high blood pressure and heart problems) 
• Theophylline (an asthma drug) 
• Voriconazole (a drug used to treat fungal infections)  

Interactions with over-the-counter drugs 

When people think about drug interactions, they often think about prescription drugs. But some drugs that are available over the counter without a prescription can interact with supplements, too.  

• A variety of herbs may interact with aspirin to increase the risk of bleeding. 
• Concentrated green tea supplements interact with pseudoephedrine, a decongestant. 
• St. John’s wort interacts with fexofenadine (Allegra). 

If you’re considering taking both an over-the-counter drug and a dietary supplement, it’s a good idea to talk with your healthcare provider or a pharmacist about possible interactions. 

When drug-supplement interactions are especially important 

There are two situations when drug-supplement interactions can be especially important: 

• When you’re taking a drug that has what healthcare providers call a “narrow therapeutic range” 
• When you’re going to have surgery. 

In these situations, it’s particularly important to talk with all your healthcare providers about the dietary supplements you’re taking now and any you may be considering taking in the future. 

Drugs with a narrow therapeutic range 

Having the right amount of certain drugs in your body is crucial. If the amount of the drug is even a little too low or too high, it can cause big problems. 

Drugs like these are said to have a “narrow therapeutic range” or “narrow therapeutic index.” 

Interactions are of special concern for drugs with a narrow therapeutic range. 

Examples of drugs with a narrow therapeutic range  

• Carbamazepine (used to prevent seizures)  
• Cyclosporine (used to prevent organ transplant rejection) 
• Digoxin (used to treat heart problems) 
• Levothyroxine (used to treat thyroid problems) 
• Phenytoin (used to prevent seizures) 

• Warfarin (an anticoagulant — also called a blood thinner)  

If you’re taking a dietary supplement, and your healthcare provider prescribes a drug with a narrow therapeutic range, tell your healthcare provider that you’re taking the supplement and ask the provider what you should do. 

If you’re going to have surgery 

If you’re going to have surgery, talk to your healthcare providers as far in advance of the operation as possible and tell them about all dietary supplements that you’re taking. 

Some dietary supplements may cause problems during surgery because: 

• They may affect your response to anesthetics or to other medicines that you may be given before, during, or after the operation. 
• They may increase your risk of bleeding (for example, fish oil supplements). 

Some healthcare providers will ask patients to discontinue all herbal supplements several weeks before having elective surgery (surgery that can be scheduled in advance). 

If you’re having an emergency operation, you won’t have a chance to stop taking supplements ahead of time. But it’s still important for you or a family member to tell your surgeon and anesthesia provider about all dietary supplements that you’re taking so that they can be prepared for any problems that might occur. 

Here’s a hint for your next visit to a healthcare provider 

When you visit a healthcare provider, it’s a good idea to bring a written list of 

• All the drugs and supplements you take. 
• How often you take them. 
• The doses you take. 

But there’s something else you may also want to do, especially if you take any products that have multiple ingredients. 

Bring the bottles of the products to the healthcare provider’s office. 

If you have the labeled bottles, any questions about what’s in your dietary supplements can be answered right away. 

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Source: The National Center for Complementary and Integrative Health