The hidden chemicals in so-called ‘herbal’ diet pills

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  • Published: May 1, 2016
  • Author: Ryan De Vooght-Johnson
  • Channels: Laboratory Informatics / Chemometrics & Informatics
thumbnail image: The hidden chemicals in so-called ‘herbal’ diet pills

The danger of diet pills

In the Western world, food is more available than ever. As a result, obesity is on the rise. Obesity rates have more than doubled since 1980 and in 2014 over 1.9 billion people were overweight.

In the Western world, food is more available than ever. As a result, obesity is on the rise. Obesity rates have more than doubled since 1980 and in 2014 over 1.9 billion people (almost 40% of all adults) were overweight.

For those who grimace at the thought of a restrictive diet, and for those who simply need to lose weight more quickly than natural means would allow, anti-obesity medications are a boon.

However, as these drugs meddle with fundamental bodily processes, many have been withdrawn owing to safety concerns, including psychiatric side effects and even reported strokes. As it stands there is only one prescription drug – orlistat – available for treatment of obesity in Europe.

With limited options, many patients have turned to herbal medicines, which are assumed to be safer to use. But because these drugs are often bought online, they can escape the rigorous quality control process of prescription pharmaceuticals. So, despite being marketed as natural, they sometimes contain illicit compounds, such as appetite suppressants, stimulants, laxatives and even anti-depressants. They may also avoid recrimination by using analogues of banned drugs. Several analogues of the now banned appetite suppressant sibutramine (which increases risk of heart attack and stroke) have been detected in non-prescription weight loss pills.

With the consumption of these pills on the rise, there is an urgent need to monitor them for banned and potentially dangerous substances.

Picking out patterns

In a study newly published in Drug Testing and Analysis, researchers from the Scientific Institute of Public Health in Belgium describe a method to analyse non-prescription slimming aids using a fingerprinting approach.

Fingerprinting – characterising the chemical composition of samples to generate a specific and recognisable pattern – is frequently used in the analysis of natural medicines. Several studies have used fingerprinting for quality control of herbal supplements, and often in combination with chemometrics approaches – which pick out patterns and useful information from chemical data.

These researchers used ultra-high performance liquid chromatography alongside photodiode array detection (UPLC-PDA) and UPLC mass spectrometry (UPLC-MS) to analyse diet pill samples. They also used two types of chemometric analysis: an ‘unsupervised’ technique based only on computer analysis (with no extra input from the researchers) to detect patterns in the data, and two ‘supervised’ techniques, which the scientists used to classify the samples and predict the identity of unknown samples.

The method was tested on herbal supplements confiscated by customs officers at Belgium’s international airport. The samples were confiscated from packages addressed to Belgian residents, which were most likely ordered online. In total, the fingerprints of 92 different slimming aids were obtained.

The samples were found to contain several dangerous substances, including sibutramine, phenolphthalein (a laxative with possible carcinogenic properties) and the stimulant amfepramone. Hierarchical cluster analysis (an unsupervised chemometrics technique) separated the samples based on their chemical content, and provided the basis for a classification system that was used by the next stage (supervised data analysis).

Overall, reliable chemometric models were obtained using photodiode array detection (PDA), total ion chromatograms (TIC) and mass spectral fingerprints. Although mass spectrometry could not classify the samples as accurately as PDA, it detected sibutramine where the PDA and TIC fingerprints could not, and was therefore the best method of fingerprinting.

Importantly, the vast majority of samples analysed contained chemical compounds, despite their herbal claims. The researchers say the public should be informed of the risk of ingesting banned substances via herbal supplements. They say packages are often fraudulently labelled, meaning patients are not aware of the health risks.

Automated classification system

The fingerprinting method described here could be a useful tool in the fight against unregulated diet pills, as they can reveal the presence of illicit compounds and give a reliable indication of the health threat they pose. Furthermore, because the models can be programmed, they can interpret lots of complex data without the need for human input, enabling automated data analysis. Looking ahead, the researchers foresee a classification system that can immediately describe the health threat of known samples and very quickly predict the threat posed by unknown ones.

Related Links

Drug Test. Analysis, 2016, Early View paper. Custers et al., Clustering and diagnostic modelling of slimming aids based on chromatographic and mass spectrometric fingerprints.

WHO: Obesity and overweight

Article by Ryan De Vooght-Johnson

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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