rac-O-Methyltolterodine fumarate is primarily used in the treatment of overactive bladder (OAB) syndrome. This condition is characterized by symptoms such as urinary urgency, frequency, and incontinence. The compound works by blocking muscarinic receptors in the bladder, which helps to reduce involuntary bladder contractions. This leads to improved bladder control and a decrease in the frequency of urination. It is often incorporated as an active pharmaceutical ingredient (API) or reference standard in formulations when lifestyle changes and other non-pharmacological treatments have not been effective.