Sibutramine, an obesity medicine, was the most common adulterant detected.
The systematic review looked at the findings of 26 English-language published studies on adulterants in health supplements.
Of which, 23 studies - equivalent to 88.5 per cent - had identified sibutramine as the most common adulterant.
Other adulterants detected include the laxatives sennosides, phenolphthalein, seizure medication fenfluramine, edema medication bumetanide, antidepressants fluoxetine, paroxetine, sertraline, bupropion, and caffeine.
Findings were published in the journal Frontiers in Pharmacology. The research was a collaboration between institutions from Thailand, Vietnam, Taiwan, and the UK.
The research focused on studies on synthetic pharmaceutical adulterants in weight-loss natural products published between 2012 and 2021.
Examples of natural weight-loss products assessed in include slimming tea, and products in supplement formats, such as powder and tablets.
Notably, the prevalence of adulteration has declined in the early 2020s as compared to the years prior.
Studies between 2020 and 2021 reported a lower median prevalence rate of adulteration at 23.3 per cent.
In contrast, the rate of adulteration in papers published between 2016 and 2018 was 2.3 times higher at 54.4 per cent.
Between 2012 and 2014, the rate of adulteration was also higher than the 2020s at 45.9 per cent.
Chromatographic methods are the most commonly used in detecting adulteration, accounting for 77 per cent of the 26 studies.
The other methods used were spectroscopic techniques and electrophoretic methods.
“This systematic review and meta-analysis highlighted that around one-third weight-loss natural products were adulterated by synthetic drugs based on chemical laboratory-studies,” said the researchers.
The two extremes: Pharmacies and local markets
Samples collected from pharmacies had the lowest prevalence of adulteration at 14.8 per cent.
In contrast, samples from local markets showed the highest prevalence of adulteration at 79.4 per cent.
Adulteration is second most detected in internet purchases at 35.8 per cent.
Products from herb or grocery stores ranked third at 27.7 per cent, followed by those from community pharmacies.
Prevalence of adulteration highest in Europe
The highest prevalence rate of adulteration was observed in Europe, with a median of 54.7 per cent, followed by the Middle East at 41.3 per cent.
America came in third at 31.1 per cent, followed by Asia at 24.7 per cent.
Most of the 26 studies assessed in this systematic review were from Asia (nine studies).
Seven were from Europe, six were from the Middle East, three were from America, and one from Africa.
However, due to a lack of sufficient information, the researchers said they were unable to gather detailed data on weight-loss products such as brands, origins, and herbal components.
“Such information provides essential insights for healthcare providers and regulatory agencies in overseeing the importation and supply of these products, particularly given that preparations originating from Asia have been reported as the most adulterated,” said the researchers, citing a study by Posadzki et al published in 2013.
Source: Front Pharmacol.
From ‘traditional’ remedies to ‘modern’ supplements: a systematic review and meta-analysis of pharmaceutical adulteration in weight-loss natural products.
DOI: 10.3389/fphar.2025.1594975.
Authors: Phan DTA, Kongkaew C, Heinrich M, Dao TCM, Vo TH.
