Daily Tadalafil as Adjunctive Therapy Versus Monotherapy for PDE5 Inhibitor-Resistant Erectile Dysfunction

Inclusion Criteria * Age: 18 to 70 years. * Diagnosis: Erectile dysfunction for at least 6 months. * PDE5 inhibitor resistance: History of on-demand PDE5 inhibitor use for at least 3 months with inadequate response, defined as: * International Index of Erectile Function-Erectile Function score less than 26 despite optimal dosing. * Self-reported inability to achieve or maintain an erection sufficient for satisfactory sexual intercourse in at least 50% of attempts. * Confirmed proper medication use with at least 4 to 8 attempts with adequate sexual stimulation. * Stable relationship: Sexually active with a female partner for at least 6 months. * Informed consent: Willing and able to provide written informed consent. Exclusion Criteria * Current use of nitrates. * Unstable cardiovascular disease, including recent myocardial infarction within 6 months, unstable angina, or severe heart failure. * Uncontrolled hypertension greater than 180 over 110 mmHg or severe hypotension less than 90 over 50 mmHg. * Severe hepatic impairment, Child-Pugh class C, or renal impairment with estimated glomerular filtration rate less than 30 mL per minute per 1.73 m². * Untreated hypogonadism, total testosterone less than 250 ng/dL. * Severe penile anatomic deformity or prior penile prosthesis. * History of priapism. * Severe untreated depression. * Pelvic surgery or radiation within 6 months.