Drugs for the treatment of obesity show significant effectiveness, but the adverse effects (ADRs) of these drugs are numerous and varied, and some of them are highly cost-generating. Our research aimed to define the health care utilization pattern in treating ADRs of antiobesity therapy, to compare the costs of treating these ADRs among selected European countries, and to identify the key cost drivers. A comparative analysis of the costs of treating the ADRs of antiobesity drugs in 10 European countries (seven EU members and three from the Western Balkans) was conducted, and the impact of parameters of global health expenditures on them was assessed. There are considerable differences in costs of treating adverse antiobesity drug reactions among European countries: costs of treating gastroesophageal reflux disease varied almost 20 times between North Macedonia (12.6 EUR) and Estonia (202.9 EUR). The Gross Domestic Product per capita was an important cost driver in treating the majority of the ADRs studied (p < .001), except for retinopathy, anaphylaxis, and respiratory disorders. The Domestic Private Health Expenditure increased the costs of treating depression (p = .012), upper respiratory tract infection (p = .008), melanocytic naevus (p = .027), and drug-induced hepatitis (p = .023). Investment in pharmaceuticals, medical goods, and preventive care tended to reduce the costs of treating several ADRs, which are seemingly unrelated to the body site or mechanism. Healthcare utilization and costs of treating ADRs to antiobesity drugs vary significantly among European countries. These differences should be considered when creating inputs for cost-effectiveness and budget impact models to decrease their uncertainty.