An estimated 1.3 million older Britons may be putting themselves at risk by taking alternative therapies which could potentially interact with their prescribed drugs, a new study suggests.

GPs should ask their patients about herbal and supplement usage to identify potential side effects, according to the authors of a small study published in the British Journal of General Practice.

Researchers polled 155 people over the age of 65 who were taking at least one prescription drug.

One in three (33.6%) were found to also be taking herbal medicinal products or dietary supplements alongside their prescription medicine.

These patients took between one and eight additional products, with women more likely to take them than men.

The most commonly used dietary supplements were cod liver oil, glucosamine, multivitamins, and vitamin D.

While common herbal medicinal products were evening primrose oil, valerian, and a branded herbal product that includes hops, gentian, and passion flower.

Researchers from the University of Hertfordshire identified that 16 participants were at risk of potential adverse drug interactions.

Potential adverse side effects of interactions can include reducing the effectiveness of the prescription medication, risk of bleeding and increased blood glucose concentrations.

“One-third of older adults in this study’s sample were using an herbal medicinal product or supplement concurrently with prescription drugs,” the authors wrote.

“About one in three concurrent users was at risk of a potential herb–drug or supplement–drug interaction.

“If applied to the UK population that would mean 1.3 million older adults in the UK are at risk of at least one potential herb–drug or supplement–drug interaction.”

They added: “GPs should routinely ask questions regarding herbal and supplement use, to identify and manage older adults at potential risk of adverse drug interactions.”

Royal College of GPs chairwoman Professor Helen Stokes-Lampard said: “Our ageing population means that more people are living longer, often with more than one long-term condition, and as a result they are often, quite appropriately, taking multiple prescribed medications in order to treat and manage these conditions.

“What’s important is that the patient’s GP is aware of all the different medicines and supplements a patient is taking, so that we can keep an eye on the way they interact with each other.

“Patients may not think to mention to their GP what herbal medications or dietary supplements they may be taking, but this research is a useful reminder that patients should disclose all of the medication they are using, including any natural or herbal drugs, so that the GP can weigh up all of the benefits and risks and advise of any potential adverse interactions.

“GPs do have concerns about the over-medicalisation of patients and that’s why we are working with them to ensure they are only taking the medication they really need and that have evidence of benefit, so that they can live the best possible quality of life and not spend money on supplements that won’t help and may in fact cause harm.

“Another way GPs are encouraging patients to be healthy is by recommending activities such as community or volunteer groups, or exercise classes, so that patients are doing their very best to reduce reliance on medication for conditions which are lifestyle-related.”