Check every prescription medicine, over-the-counter drug, vitamin, mineral, herbal remedy, and other supplement for interactions before you start, stop, or change a product. These combinations can make a medicine work less well, increase side effects, or change how the body handles it. Ask your pharmacist or prescriber to review your full list, including doses and how often you take each item, and follow the product labels.
What Are Drug Interactions, and Why Do They Matter?
A drug interaction happens when a medicine's effects change because of another medicine, a supplement, a food or drink, or a health condition. According to MedlinePlus, interactions can make medicines less effective, increase side effects, or change how one or both substances work.
Interactions do not always cause noticeable symptoms. In some cases, a medicine may become less effective without an obvious warning. In others, the combination may increase the risk of unwanted effects. A product described as natural, herbal, traditional, or plant-based can still affect prescription medicines.
Checking interactions is especially important when you use several medicines, receive prescriptions from different clinicians, or regularly take supplements. A pharmacist can review the complete combination rather than assessing each product in isolation.
Which Prescription and Natural Product Interactions Should You Check First?
Some combinations are particularly important to review because they may increase bleeding, affect medicine levels, or interfere with treatments that need to work reliably. The examples below highlight interactions worth discussing with a healthcare professional. They are not a complete list, and the risk depends on the exact products involved.
- Blood thinners and herbal supplements: Products such as ginkgo may increase bleeding risk when taken with medicines such as warfarin.
- Antidepressants and St. John's wort: This herb can reduce the effectiveness of some medicines and may increase serotonin-related side effects when combined with certain antidepressants.
- Hormonal contraception and herbal remedies: St. John's wort can reduce the effectiveness of some birth control pills.
- Transplant, seizure, HIV, and cancer medicines: St. John's wort can interact with several medicines in these groups, potentially reducing their effects.
- Heart, cholesterol, blood pressure, and diabetes medicines: Some herbal extracts and concentrated supplements can change the way these medicines work or the amount present in the body.
- Medicines with a narrow therapeutic range: Drugs such as digoxin, cyclosporine, and warfarin may require particular care because relatively small changes in their levels or effects can have important consequences.
The National Center for Complementary and Integrative Health (NCCIH) highlights St. John's wort, goldenseal, concentrated green tea supplements, and certain other herbs as products that may interact with specific medicines. The strength of the evidence differs between products, so a pharmacist should assess the particular combination rather than assuming that every supplement has the same risk.
How Can Herbal Products Change the Effects of Prescription Medicines?
St. John's wort: A supplement with many known interactions
St. John's wort is commonly marketed for mood-related concerns, but it can interact with a wide range of prescription medicines. It can speed up processes that break down certain drugs, reducing their levels and potentially making treatment less effective.
According to the NCCIH's St. John's wort safety information, documented concerns include interactions with some antidepressants, birth control pills, warfarin, transplant medicines, certain seizure medicines, some heart medicines, HIV medicines, cancer medicines, and certain statins. Combining the herb with specific antidepressants or other medicines that affect serotonin may also cause potentially serious serotonin-related side effects.
Tell your prescriber before using St. John's wort, even if you have taken it previously without a problem. Do not assume that a low dose, a different brand, or several hours between products removes the interaction risk.
Ginkgo and blood-thinning medicines
Ginkgo is sold in supplements promoted for memory and other health purposes. However, its use alongside anticoagulant medicines such as warfarin may increase the risk of bleeding. The NCCIH's ginkgo safety information specifically identifies this potential interaction and recommends discussing herbal products with a healthcare professional when taking medicines.
People who take blood thinners should mention all herbal capsules, extracts, teas, and combination supplements they use. The exact product matters, and the risk cannot be judged reliably from the word "natural" on a label.
Green tea extracts, goldenseal, and other concentrated supplements
Herbal products can also affect medicines that are not usually associated with supplement use. For example, concentrated green tea supplements may lower blood levels of certain medicines, including nadolol, a beta-blocker, and atorvastatin, a cholesterol-lowering medicine. Goldenseal may alter how the body processes medicines such as metformin, which is used to manage blood glucose.
These examples concern particular supplements and medicines; they do not mean that ordinary foods and all products made from the same plant have identical effects. Bring the exact supplement label to your pharmacist so the ingredients, formulation, and dose can be checked.
What Other Drug Interactions Should You Look For?
Prescription medicines combined with over-the-counter products
Over-the-counter medicines can interact with prescriptions just as supplements can. Pain relievers, cold and flu remedies, antihistamines, sleep aids, antacids, and decongestants may contain ingredients that require extra care with certain medicines or health conditions.
For example, combining some sedating medicines can increase drowsiness and slow reaction times. Alcohol can also increase drowsiness or other unwanted effects with certain medicines. Some over-the-counter products contain several active ingredients, so using more than one product may result in unintended duplication.
The U.S. Food and Drug Administration (FDA) recommends reading medicine labels for interaction warnings and discussing prescription drugs, nonprescription medicines, vitamins, minerals, botanicals, herbal products, and foods with a doctor or pharmacist.
Vitamins, minerals, and nutritional supplements
Vitamins and minerals should also be included in an interaction review. A product does not need to contain an herb to affect medicine use. Multivitamins, mineral supplements, concentrated nutrition products, and products containing several active ingredients may raise questions about compatibility, dose, or timing.
Do not assume that a supplement is safe to combine with a medicine simply because it is sold without a prescription. When a vitamin or mineral has been recommended to address a documented deficiency, tell the clinician who manages your medicines so the full combination can be reviewed.
Food, drinks, and existing health conditions
Some medicines interact with particular foods or beverages, while other medicines may be unsuitable for people with certain health conditions. For example, grapefruit can interact with some medicines, and certain decongestants may be unsuitable for people with high blood pressure or specific heart conditions.
Check the instructions for each medicine to find out whether you need to avoid particular foods or drinks or take a product with food. Do not apply a general rule to every medicine in the same category; interaction advice can differ between individual drugs.
How Do You Check Whether Two Products Can Be Taken Together?
A reliable interaction check starts with a complete and accurate list of everything you take. Review that list whenever a new medicine is prescribed, a dose changes, you start a supplement, or you discontinue a product.
- Make a full medication list. Include prescription drugs, over-the-counter medicines, vitamins, minerals, herbal remedies, traditional products, powders, gummies, and combination supplements.
- Record the details. Write down each product's name, active ingredients, dose, how often you take it, and when you started using it. Include products used only occasionally.
- Check the packaging and patient information. Read the interaction warnings and instructions about food, alcohol, other medicines, and supplements. For prescription medicines, review the patient leaflet supplied with the medicine.
- Ask a pharmacist or prescriber to review the combination. Provide the exact product names and doses, particularly when an ingredient list includes multiple herbs or proprietary blends.
- Confirm the instructions before changing anything. Ask whether the products should be avoided, whether a different product is more suitable, and whether any monitoring or timing changes are needed.
An online interaction checker can be a useful starting point, but it should not be treated as proof that a combination is safe. Available information differs between medicines and supplements, and not every possible interaction has been studied adequately. A pharmacist can interpret the available evidence in the context of your treatment and medical history.
What Information Should You Give Your Pharmacist?
Bring the medicine containers or clear photographs of their labels whenever possible. Brand names alone may not reveal all active ingredients, particularly in combination products or supplements sold under different formulations.
Tell your pharmacist about any relevant medical conditions, allergies, pregnancy or breastfeeding, and any recent changes in your medicines. Mention planned surgery or procedures, too, because some medicines and supplements may affect procedural safety or the instructions you need to follow beforehand.
Useful questions include:
- Could any of these products make another medicine less effective or increase its side effects?
- Do any ingredients overlap between my prescriptions, pain relievers, cold remedies, or supplements?
- Do I need to avoid a product, change its timing, or have any tests or monitoring?
- What should I do if I notice a possible side effect after starting a new product?
For children, extra care is important because the safety of many herbal products has not been established adequately. The NHS notes that herbal medicines are not recommended for children and that some herbal products may be unsuitable during pregnancy or breastfeeding and for people with kidney or liver problems. Seek advice from an appropriate healthcare professional before using these products in these circumstances.
What Should You Do If You Have Already Taken a Possible Combination?
Taking two products that may interact does not automatically mean that harm has occurred. The next step depends on the medicines involved, their doses, when they were taken, and your circumstances.
Contact your pharmacist or prescriber promptly for product-specific advice. Do not stop, double, or change a prescribed dose on your own to compensate for a possible interaction. If you develop a concerning new symptom after taking a combination, explain which products you used and when. Seek emergency medical care for symptoms such as difficulty breathing, fainting, or serious bleeding.
Keeping an updated medicine list and checking each new product before use can help prevent avoidable interactions. The most dependable approach is to review the whole combination with a healthcare professional rather than judging products individually.