Complementary medicine risks: an interview with Dr Andrew Boyden, NPS MedicineWise


What are complementary medicines? Are they different to alternative medicines?

Complementary medicines include products containing herbs, vitamins, minerals, nutritional supplements, homoeopathic medicines, certain aromatherapy products and traditional Chinese medicines. For this reason they are also called herbal, natural or alternative medicines.

Complementary medicines are medicines because they contain substances that are meant to change the way your body deals with illness or injury or to maintain your health and wellbeing.

Do multivitamins class as complementary medicines?

Multivitamins are considered complementary medicines. They typically contain various vitamins and minerals, but many also contain other complementary medicines such as herbs.

Do complementary medicines undergo as much testing as other medicines?

Some complementary medicines have been tested in good quality scientific trials to show that they are effective, but most have not.

Compared with prescription and pharmacy medicines, complementary medicines undergo less testing in general, so less is usually known about their effectiveness.

Are complementary medicines as powerful as prescription medicines?

Complementary medicines are often considered less powerful than prescription medicines. But like all medicines they should be treated with care.

Complementary medicines can still cause side effects in some people, and may interact with other medicines and food, sometimes with potentially harmful effects. This is the case even when the medicine comes from a ‘natural’ source and is available over the counter or from supermarkets, health food shops or other stores, or from herbalists, naturopaths and the internet.

Do people treat complementary medicines as carefully as prescription medicines?

We know that many people don’t consider complementary medicines as medicines. In fact, less than half of people surveyed in an Australian census of medicines use by NPS MedicineWise considered certain vitamins and herbs — like multivitamins, echinacea and fish oil — to be medicines.

There may be many reasons for this. Supermarket, health food store and pharmacy shelves are packed with an array of natural, herbal and alternative medicines, so many people assume they must be safe.

And many people may consider complementary medicines as safe, without potential side effects and other problems, because most products have a natural source.

What kinds of side effects can complementary medicines cause?

Complementary medicines can cause a range of side effects depending on the medicine or product. For example valerian — a herb sometimes used for sleep problems and anxiety — can cause headaches, excitability and vivid dreams. St John’s wort — found in many complementary medicine products used to alleviate depression — can cause dry mouth, dizziness, diarrhoea, nausea, increased sensitivity to sunlight, and fatigue.

And side effects aren’t only possible with products you take orally, such a tablet, capsule or liquid. For example zinc lozenges, used for cold symptoms, can cause nausea or a bad taste in the mouth.

Some side effects can also be serious or more problematic for an individual than others. Echinacea for example — which is sometimes used to try to ward off infections and reduce the duration of colds — may worsen asthma in some people. And some glucosamine products are derived from shellfish and may cause a reaction in people who are allergic to shellfish.

What are some of the cases where complementary medicines could mix badly with prescription medicines?

A number of complementary medicines, including herbs, multivitamins and nutritional supplements, may interact with prescription and pharmacy medicines to reduce how well they work or cause negative effects.

St John’s wort is a prime example. This herb can interact with several commonly used prescription medicines. In most of its interactions, St John’s Wort can make the other medicine less effective. This is the case with:

  • birth control pills (oral contraceptives)
  • warfarin and other medicines used to thin the blood
  • epilepsy medicines
  • digoxin, a medicine used for heart conditions
  • HIV medicines
  • chemotherapy medicines
  • medicines used to prevent rejection after an organ transplant.

St John’s wort may also interact with some antidepressants and increase the risk of side effects including serotonin toxicity, which can be serious.

Taking high doses of omega-3 fatty acids (more than 2 g daily) in fish oil supplements may make your blood take longer to clot. If you’re taking other medicines that also affect blood clotting, such as warfarin or aspirin, you could increase your risk of bleeding problems, such as stomach or bowel bleeding.

Supplements containing the minerals calcium, iron, magnesium or zinc can reduce the absorption of certain prescription medicines through the gut, including some antibiotics and bisphosphonate medicines used for osteoporosis (e.g. alendronate, brands include Fosamax). This means that if you’re taking a multivitamin or other product containing any of these minerals, you’ll need to take them separately to these other prescription medicines (usually at least 2 hours apart).

Are there other examples of possible interactions and side effects when people take multivitamins or other supplements?

People who have, or have had, a kidney stone should not take more than 1000 mg of vitamin C a day, because this greatly increases the chance that kidney stones will recur. The amount of vitamin C you take in a multivitamin each day may be well below 1000 mg. But if you take more than one product containing vitamin C, it could all add up to more than the maximum daily dose that’s right for you.

Multivitamin preparations may contain vitamin K. If you also take warfarin, vitamin K can oppose its effects and possibly increase your chance of a blood clot. The amount of vitamin K in a multivitamin may be smaller than other preparations, but you may also be consuming vitamin K in your diet or in other multivitamins, and this could add up to an amount that interacts with your warfarin.

Serious cases of high potassium levels, which can affect the heart, have occurred when potassium supplements have been taken with other medicines that can also increase potassium levels in your blood. These include some medicines used for high blood pressure and heart failure, some anti-inflammatory medicines, and some glucosamine products containing potassium. Some multivitamin preparations contain potassium.

Are there other risks for people taking complementary medicines?

Many multivitamins and other complementary medicines are available in a variety of strengths, and they may often contain several active ingredients. So keep in mind that if you change from one brand to another, it may contain a higher dose of the active ingredients. This may mean it has a stronger effect on your body or other medicines you take, and may trigger an interaction or side effect that you did not have before.

The right dose may also depend on whether the complementary medicine is for an adult or a child, and may depend on what you’re taking it for. This is why it’s important for people to follow the recommendations given by their doctor, pharmacist or other qualified health care provider, or as provided on the medicine label or packaging.

It’s also crucial that people not to be tempted to take or give more the recommended dose, especially without talking to their health professional first, as there can be safety implications.

Should you always tell your health professional about any complementary medicines you are taking?

Absolutely, this is really important to help you avoid potentially harmful interactions with your other medicines, and possibly side effects.

For instance, if you take a multivitamin containing potassium and vitamin K, it may cause problems if you’re also taking warfarin and a medicine for high blood pressure that can increase potassium levels. Even if the amount of potassium in the multivitamin is small, it’s essential that your doctor know you’re taking it along with your blood pressure lowering medicine – they may need to check your blood potassium level. Many things can also affect warfarin so your health professional needs to know about every medicine you take (including multivitamins) and any changes in your lifestyle (such as a new diet), so they can test that it isn’t affecting how well your warfarin works.

Despite the importance of telling your health professionals about your other medicines, many people don’t. An NPS MedicineWise survey of 1500 Australians in 2012 found 48% of respondents did not tell their doctor or pharmacist about their other medicines the last time they received or purchased a medicine. It’s likely that multivitamins and other complementary medicines are no exception to this.

Why are people often afraid of telling their health professional about their complementary medicines?

People may think that some doctors disapprove of complementary medicines, but this is not always the case. Health professionals know that many people use them, and even if they are not convinced that all of them are effective, they will appreciate knowing about any you are taking.

In order to treat you as best they can, health professionals need to know about all the medicines you are taking, including multivitamins — especially if there could be an interaction between a person’s medicines, or if you’re already taking other medicines that contain the active ingredients in your complementary medicine or that could increase the chance of side effects.

How has the internet changed people’s access to complementary medicines?

Indeed there are thousands of websites with information about complementary medicines and many of these are designed to sell products.

Unfortunately many websites are ‘fake’ sites, and many sell out-of-date, poor quality, contaminated or even fake medicines. Sorting out the ‘good’ sites from the ‘bad’ ones isn't always easy, but there are a few simple rules to point you in the right direction.

Firstly it is best to seek advice from a qualified person when choosing a complementary medicine. Buying an unfamiliar medicine over the internet without being able to talk to a health professional puts you at risk of taking a medicine that is not suitable for you, has undesirable side effects, or interacts with your other medicines.

If you decide to buy a medicine online, avoid websites based overseas. Overseas medicines may not meet Australia's strict quality and safety standards. It is also illegal for some medicines to be brought into Australia by post.

Never buy medicines from a website that does not give its full postal address. It could be a fake site. The site should also provide a telephone number so you can contact them if there is a problem.

And always beware of sites that offer revolutionary, new or miracle cures, or cures whose effectiveness is guaranteed. If it sounds too good to be true, it probably is!

Where can readers find more information?

Your doctor, pharmacist or other health professional can help answer questions for you about multivitamins and other complementary medicines. In Australia you can also call NPS Medicines Line on 1300 MEDICINE (1300 633 424) to get information from a health professional about your prescription, over-the-counter and complementary medicines (Monday–Friday, 9am–5pm AEST, excluding public holidays).

There is a range of information about complementary medicines available on the NPS MedicineWise website. The website also provides information about buying medicines, including tips when you’re searching the internet.

About Dr Andrew Boyden

Andrew Boyden BIG IMAGEAndrew studied medicine at the Flinders University of South Australia and has further qualifications in general practice and public health.

Prior to being appointed as clinical advisor with NPS MedicineWise he has worked in health advisory and management roles  with  both government and non-government organisations -  including over several years as national director of clinical issues for the National Heart Foundation of Australia.

He is interested in the delivery of evidence-based medicine and quality healthcare.  He continues to undertake part-time general practice.

April Cashin-Garbutt

Written by

April Cashin-Garbutt

April graduated with a first-class honours degree in Natural Sciences from Pembroke College, University of Cambridge. During her time as Editor-in-Chief, News-Medical (2012-2017), she kickstarted the content production process and helped to grow the website readership to over 60 million visitors per year. Through interviewing global thought leaders in medicine and life sciences, including Nobel laureates, April developed a passion for neuroscience and now works at the Sainsbury Wellcome Centre for Neural Circuits and Behaviour, located within UCL.


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The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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