This study proposed a high-performance thin-layer chromatography (HPTLC) screening method to detect phosphodiesterase 5 (PDE-5) inhibitors as possible adulterant agents in various dietary supplements. Chromatographic analysis was performed on silica gel 60F254 plates using a mixture of ethyl acetate:toluene:methanol:ammonia in a volume ratio of 50:30:20:0.5 as a mobile phase. The system provided compact spots and symmetrical peaks of sildenafil and tadalafil with retardation factor values of 0.55 and 0.90, respectively. The analysis of products purchased from the internet or specialized stores demonstrated the presence of sildenafil, tadalafil, or both compounds in 73.3% of products, highlighting inadequacies and inconsistencies in the labeling, as all dietary supplements were declared to be natural. The results were confirmed using ultra-high-performance liquid chromatography coupled with a positive electrospray ionization high-resolution tandem mass spectrometry (UHPLC-HRMS-MS) method. Furthermore, in some samples, vardenafil and various analogs of PDE-5 inhibitors were detected using a non-target HRMS-MS approach. The results of the quantitative analysis revealed similar findings between the two methods, with adulterant quantities found to be similar to or higher than those in approved medicinal products. This study demonstrated that the HPTLC method is a suitable and economical method for screening PDE-5 inhibitors as adulterants in dietary supplements intended for sexual activity enhancement.

The growing popularity and consumption of herbal slimming supplements can be attributed to their perception as natural products that lack side effects. However, the composition and ingredient quality listed on their labels often undergo insufficient control. As a result, some manufacturers add undeclared synthetic pharmaceuticals to enhance weight loss effects. The synthetic adulterants, particularly the anorectic stimulants, have been associated with increased risks of cardiovascular adverse effects, posing significant health risks to consumers. This study aimed to analyze various weight loss supplements marketed as “natural” products to detect possible adulterants. A new high-performance thin-layer chromatography (HPTLC) method was used for initial screening, while gas chromatography coupled with mass spectrometry (GC–MS) served as a confirmation tool. Additionally, high-performance liquid chromatography (HPLC) was employed to analyze phenolphthalein. A total of 34 supplements acquired online or from specialty stores were analyzed. It was found that most of them contain caffeine from herbal ingredients included in the products’ formulation. Some products list the added caffeine, but the measured levels significantly exceeded the labeled values. The most commonly detected adulterants were sibutramine and phenolphthalein. These results highlighted the inadequacies and inconsistencies in labeling, as all herbal supplements were declared “natural” despite containing adulterants. Furthermore, they highlighted the suitability of the HPTLC method as an effective and cost-effective screening tool for detecting adulterants in dietary supplements.