Many herbal supplements, including for obesity and erectile dysfunction, contain hidden unlicensed pharmaceutical ingredients that could endanger people’s health, experts have warned.

The research team, from Queen’s University Belfast, Kingston University in London and the life sciences testing company LGC, concluded that not only do such supplements often make unverified claims as to their benefits but some have illegal ingredients which could pose a threat – potentially causing low blood pressure or an increased risk of heart attacks.

The substances are unlicensed medicines as they are appearing in products classified as food supplements. Among the most common substances identified was sibutramine, according to the study, published in the Journal of the Association of Public Analysts.

Sibutramine was licensed as the medicine Reductil until 2010, when it was withdrawn across Europe and the US due to an increased risk of heart attacks and strokes associated with the use of the drug.

Tadalafil and sulfoaildenafil were among the most frequently undeclared ingredients in products for erectile dysfunction. When taken with other medicines containing nitrates, they can lower blood pressure drastically and cause serious health problems.

Emeritus professor Duncan Burns, from Queen’s University’s Institute for Global Food Security, said: “We have found that these supplements are often not what customers think they are – they are being deceived into thinking they are getting health benefits from a natural product when actually they are taking a hidden drug.

“These products are unlicensed medicines and many people are consuming large quantities without knowing the interactions with other supplements or medicines they may be taking. This is very dangerous and there can be severe side effects.”

The research team analysed adverse findings recorded by the European Union’s rapid alert system for food and feed (RASFF) between 2009 and 2016 inclusive. The database is designed to inform member states who can then take appropriate action locally. Consumers can access the database but, unlike authorities in member states, they often cannot see the product names.

The experts believe the pharmaceutical ingredients are sometimes added accidentally but on other occasions deliberately in an attempt to enhance products.

They identified 63 instances of food supplements containing sibutramine between 2009 and 2016, including 47 after 2010, when Reductil was withdrawn. There were 29 instances of tadalafil being found in food supplements in the eight-year period examined and 68 of sulfoaildenafil and chemical substances similar to it.

People suffering from conditions such as diabetes and hypertension are frequently prescribed nitrate-containing medicines. Erectile dysfunction is often associated with these conditions, raising the prospect that patients may be tempted to try herbal supplements, which they do not know contain tadalafil or sulfoaildenafil, which can interact negatively with the nitrates.

Burns said: “People who take these products will not be aware they have taken these substances and so when they visit the doctor they may not declare this and it can be difficult to determine what is causing the side effects. It is a very dangerous situation.”

Another common substance was yohimbine, found in 30 supplements, which has been said to have aphrodisiac-like effects but has been known to increase blood pressure and induce anxiety.

Burns said the RASFF list was unlikely to be comprehensive “unless they went to every health food shop and every herbalist in the country”.

He advised consumers: “Be cautious about supplements you buy and use reputable websites. Discuss any concerns with your GP and always tell them what you’re taking.”