Statins are among the most prescribed drugs today, often as part of chronic polytherapy in cardiovascular patients. Despite the justified status of statins as safe drugs, it is necessary to prevent their side effects in order to ensure adherence, especially in therapies aimed at preventing cardiovascular events. Atorvastatin, a substrate of the ABCG2 transporter, is subject to variable pharmacokinetics in individuals with altered expression of this transporter. The p.Q141K variant (c.421C>A, rs2231142) is associated with reduced protein expression. This leads to increased concentrations of its substrates due to increased absorption and the inability to be excreted outside of cells where the ABCG2 acts as an efflux pump. The polymorphism of this pharmacogene could explain the dose-dependent side effects of atorvastatin associated with the musculoskeletal system, acute manifestations of liver damage, and other less common side effects. CPIC guidelines for statin prescribing relate to the SLCO1B1 gene, the first gene whose importance in the pharmacokinetics of this drug class has been recognized. To date, the influence of ABCG2 gene polymorphisms has been established in the case of rosuvastatin and allopurinol dosing, where lower and higher doses are recommended in individuals with the observed variant allele A, respectively. In this thesis, a case-control study was conducted to evaluate the association between adverse effects and ABCG2 gene polymorphisms. Genotyping of ABCG2 c.421C>A was performed using the TaqMan® DME method on a total of 223 participants receiving atorvastatin as part of therapy for various cardiovascular and metabolic diseases. The participants were dichotomized (cases vs. controls) based on whether they experienced side effects after taking atorvastatin or not. A statistically significant association between the ABCG2 c.421C>A polymorphism and reported side effects was demonstrated. Novel findings in the field of pharmacogenomics assist in assessing the risk and benefits of prescribing atorvastatin, bringing us ones step further towards personalized medicine.