Written by the Priceline Pharmacy Pacific Fair team. Reviewed by Jason Markey, BPharmSci, MPharm, Owner and Pharmacist.
General health information from a registered pharmacist. It doesn’t replace advice from your own pharmacist or doctor.
Yes, some common supplements can change how your medicines work. healthdirect warns that supplements can have side effects or interact with other medicines, making them dangerous or less effective. The best-documented examples include St John’s wort with antidepressants and the contraceptive pill, vitamin K-rich foods with the blood thinner warfarin, and minerals such as magnesium with some antibiotics and osteoporosis medicines.
The good news is that most problems are avoidable. Tell every doctor and pharmacist about everything you take, and bring it all along to a medication review. Here’s what to look out for.
Why doesn’t “natural” mean interaction-free?
Vitamins, minerals and herbal products are easy to buy, and many people don’t think of them as medicines. healthdirect points out that while dietary supplements aren’t classified as drugs, they can still cause harm, including side effects and interactions. More isn’t necessarily better either: getting more than you need of some nutrients can be harmful.
In Australia, the Therapeutic Goods Administration (TGA) regulates the sale of vitamins for safety and quality. healthdirect advises being especially careful when buying supplements from overseas.
Which supplements are known to interact with medicines?
These are some of the well-documented examples, described by type of medicine.
| Supplement or food | Medicines it can affect | What can happen |
|---|---|---|
| St John’s wort | Antidepressants and some migraine medicines (triptans) | A higher risk of toxicity, including serotonin syndrome, which can be life-threatening |
| St John’s wort | The combined oral contraceptive pill | The pill works less well, raising the risk of an unplanned pregnancy |
| St John’s wort | Some transplant, HIV, epilepsy and heart medicines | These medicines may not work properly, with risks such as organ rejection, seizures or blood clots |
| Vitamin K-rich foods, grapefruit and cranberry juice | Warfarin | healthdirect advises keeping vitamin K foods steady and avoiding grapefruit and cranberry juice |
| Magnesium supplements | Some antibiotics and some osteoporosis medicines | Less of the medicine is absorbed unless doses are spaced apart |
St John’s wort
St John’s wort is a herbal product often taken for low mood. healthdirect advises not taking it with other antidepressants, because together they increase the risk of toxicity. It also reduces the effectiveness of the combined pill, and it can affect some transplant, HIV, epilepsy and heart medicines, including warfarin.
If you already take St John’s wort with another medicine, healthdirect says to seek medical advice, and not to stop taking it before talking to your doctor. Ask your doctor or pharmacist before starting it if you use any other medication.
Vitamin K, grapefruit and blood thinners
If you take warfarin, your diet matters. healthdirect advises eating the same types of food regularly, especially foods high in vitamin K such as green leafy vegetables and the cabbage family, so your intake stays steady. It also advises avoiding grapefruit and cranberry juice, and drinking no more than 1 or 2 standard drinks of alcohol a day.
More broadly, healthdirect says blood thinners can interact with many different medicines, including ones you buy over the counter at a pharmacy, vitamins, and herbal or complementary medicines. So if you take any blood thinner, ask your pharmacist before starting a new supplement, including popular ones such as fish oil or ginkgo.
Minerals and the timing of your other medicines
Magnesium can bind to some medicines in the gut so less of the medicine is absorbed. The US National Institutes of Health (NIH) fact sheet on magnesium advises:
- taking tetracycline or quinolone antibiotics at least 2 hours before, or 4 to 6 hours after, a magnesium supplement
- separating bisphosphonates (a type of osteoporosis medicine) from magnesium by at least 2 hours
If you take calcium, iron or other mineral supplements alongside antibiotics, osteoporosis medicine or thyroid medicine, ask your pharmacist to help you plan the timing.
It works the other way too. The NIH notes that some fluid tablets (diuretics) can increase the amount of magnesium you lose, and that reflux medicines called proton pump inhibitors can cause low magnesium when taken for a long time, typically more than a year.
We’ve covered three popular supplements in more detail: vitamin D, magnesium and probiotics with antibiotics.
Who needs to take extra care?
- Older people. healthdirect notes older people are more likely to be taking medicines that can interact with each other, and suggests having your medicines checked every 6 to 12 months.
- Anyone taking a blood thinner, antidepressant, the pill, or transplant, HIV or epilepsy medicines, given the interactions above.
- Anyone having surgery or going into hospital. healthdirect advises mentioning your supplements, especially in these situations.
- Pregnant women. healthdirect warns that too much vitamin A or E from supplements during pregnancy can seriously harm the baby.
How do you stay safe with supplements?
- Keep a current medicines list that includes vitamins and other complementary medicines. healthdirect says medicine lists help make sure everyone involved in your healthcare knows what you’re taking.
- Tell every prescriber and pharmacist. healthdirect advises telling your doctor or pharmacist about any supplements before they prescribe or dispense a new medicine for you, not just your GP.
- Ask before you start or stop anything. Stopping a supplement can matter too: healthdirect advises not stopping St John’s wort before talking to your doctor.
- Never stop a prescribed medicine because of a possible interaction without talking to your doctor first.
Bring everything to a medication review
The easiest way to check for interactions is to put everything on the counter at once. Our medication reviews are a one-on-one conversation with a pharmacist about everything you take, including vitamins, herbal products and over-the-counter medicines. They’re free for Medicare card holders, take about 20 to 30 minutes, and you don’t need to book.
Bring every bottle, box and packet, including creams, drops, inhalers and anything you only take now and then. If you take a lot of medicines, your GP can also refer you for a Home Medicines Review, where a credentialed pharmacist checks your medicines at home. healthdirect notes you don’t pay for the review itself.
When to see a pharmacist or GP
Talk to a pharmacist or see a GP, such as our in-store Help Medical GPs, if:
- you take prescription medicines and want to start a new supplement or herbal product
- you’ve been taking St John’s wort with any other medicine
- you’re on the pill and have taken St John’s wort, as you may need extra contraception advice
- you’ve noticed new side effects, or a usual medicine seems to work differently, since starting a supplement
- you take a blood thinner and notice unusual bruising, bleeding gums, nosebleeds, red or brown urine, red or black stools, or heavier periods than usual
Call 000 in an emergency. If someone has bleeding that won’t stop, coughs up or vomits blood, or becomes suddenly and severely unwell after combining medicines and supplements, call triple zero (000).
Sources
This article is general information only and isn’t a substitute for personal advice from your doctor or pharmacist. Always read the label and follow the directions for use. If symptoms persist or you’re worried, talk to your pharmacist or GP. In an emergency, call 000.
Talk to our pharmacists at Pacific Fair
Pop in, no appointment needed. We’re on the ground floor of Pacific Fair Shopping Centre, Broadbeach, open 7 days and until 9pm on Thursdays.