The goal of this clinical trial is to examine the genetic markers of erectile dysfunction degree in patients with diabetes and find new predictive models based on genetic factors, with which we will be able to more accurately address the adequacy of treatment in patients with diabetes, and thus have a long-term impact to reduce side effects of treatment. We will look for a predictive model based on genetic analysis to determine in the future patients with a good response to treatment with phosphodiesterase type 5 inhibitors, in our case tadalafil 5 mg daily. The main questions it aims to answer are: 1. Genetic alterations in the NO signaling pathway affect the degree of erectile dysfunction and the response to tadalafil treatment in patients with diabetes. 2. Genetic alterations in the folate pathway affect the degree of erectile dysfunction and the response to tadalafil treatment in patients with diabetes. 3. Genetic factors of the vascular wall influence the degree of erectile dysfunction and the response to tadalafil treatment in patients with diabetes. 4. Genetic changes in the pathways of tadalafil metabolism and action influence the response to the treatment of erectile dysfunction in patients with diabetes. Participants will take the drug tadalafil 5 mg every day for three months. The level of erectile dysfunction will be assessed with the IIEF-5 questionnaire at the beginning of the study and after three months of taking the drug.