Background: The UK National Health Service (NHS) propose the use of oxybutynin prior to onabotulinumtoxinA (Botox) in the management of overactive bladder syndrome (OAB). Oxybutynin is costly and associated with poor adherence, which may not occur with Botox. We conducted a cost-utility analysis (CUA) to compare the medications. Methods: we compared the two treatments in quality-adjusted life years (QALYS), through the NHS’s perspective. Costs were obtained from UK-based sources and were discounted. Total costs were determined by adding the treatment cost and management cost for complications on each branch. A 12-month time frame was used to model the data into a decision tree. Results: Our results found that using Botox first-line had greater cost utility than oxybutynin. The health net benefit calculation showed an increase in 0.22 QALYs when Botox was used first-line. Botox also had greater cost-effectiveness, with the exception of pediatric patients with an ICER of £42,272.14, which is above the NICE threshold of £30,000. Conclusion: Botox was found to be more cost-effective than antimuscarinics in the management of OAB in adults, however less cost-effective in younger patients. This predicates the need for further research to ascertain the age at which Botox becomes cost-effective in the management of OAB.