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Obesity, a chronic disease, is associated with comorbidities such as diabetes, hypertension, cardiovascular diseases, metabolic syndrome, and stroke. In this context, the consumption of natural weight-loss ingredients as alternative obesity treatments has been increasing because of the common idea indicating that they as natural products pose no risks to human health. (Simultaneously with the widespread prevalence of obesity; the use of herbal slimming products as an alternative treatment for obesity has increased. Because, the general belief is that plant products are safe for human health.) The analyses (analysis) of phytotherapeutic formulations showed increasing numbers of counterfeit drugs, as adulterants, withdrawn from the market due to significant side-effects and a high potential for addiction threatening public health. Because the drugs used in the products are not listed on the labels, consumers do not become aware of the risks. (Because the active ingredients in these products are not listed on the label, consumers remain unaware of their risks and side effects.) These products can cause serious health side-effects due to accidental abuse, overuse, or interaction with other drugs. The illegally added adulterants are commonly including stimulants (ephedrine, caffeine), anorexic (amphe­tamine and its analogs), antidepressants (sibutramine, fluoxetine), anxiolytics (benzodiazepines), diuretics (bumetanide), laxatives (phenolphthalein), rimonabant, orlistat, and thyroid hormones. This review study aimed to describe various categories of synthetic drugs frequently added illegally into natural weight loss products as adulterants,