23 May 2019

Updated guide outlines risks of ‘natural’ interactions

Medications

An update of a complementary medicine interactions guide has added 173 possible risks for patients who take alternative medicines alongside conventional drugs.

The Blackmores Complementary Medicines Interactions Guide, allows medical practitioners to search peer-reviewed evidence of interactions for 75 of the most-common complementary medicine ingredients.

But Associate Professor Lesley Braun, director of the Blackmores Institute, warned GPs using the guide should be aware not all evidence used in the guide was based on clinical studies.

“We try and put into our database what is the evidence and then interpret it based on the strength of evidence, so we don’t become alarmists and extrapolate from test-tube studies which aren’t relevant,” she said.

Evidence in the guide is ranked according to the likelihood of an interaction occurring, the severity of the interaction and the level of evidence evaluated to inform this knowledge.

For example, some of the interactions which have only been tested in animal studies include interactions between the plant red clover and tamoxifen, and vitex (also called chasteberry), which may lower the efficacy of oestrogen-containing contraceptive drugs.

The spectrum of evidence – “A” being at least one good quality randomised, placebo-controlled trial or meta-analysis or systematic review, and “D” being an in-vitro or animal study – is accompanied by a summary of whether the evidence is strong enough to prompt intervention by a healthcare professional.

Professor Braun said the most common searches of the Blackmores guide by GPs were to check for interactions with drugs such as warfarin or digoxin, which had narrow therapeutic indexes. 

“Any drug with a narrow therapeutic index is more prone to have a drug interaction regardless because a small level change can have a big impact,” she said.

The Blackmores Institute says the guide is designed help GPs become more familiar with some of the most commonly used over-the-counter vitamins and supplements patients might be taking.

Recent research by of the University of Technology in Sydney shows only that only one in three people taking complementary medicines tell their doctors about that use.

The reasons for patients not revealing use of complementary medicines included thinking their doctor will disapprove; the doctor not asking; or the patient believing the doctor won’t know enough about the therapy. 

Patients’ perceptions of how doctors might respond to them using alternative therapies was an important factor in whether or not they would disclose that practice, the research found.

The guide can be found at: www.blackmoresinstitute.org/interactions