Spinal cord injury is a major cause of lifelong morbidity. Functional micturition problems are common while the management choices are comparatively narrow. Some patients are refractory to the combination of the available therapeutics, namely the anticholinergics and a beta-adrenergic named mirabegron. In this paper we report our results of using gabapentin as an add-on treatment in the refractory overactive detrusor cases secondary to spinal cord injury. Material and Methods A total of 27 patients who had spinal cord injury between the levels of second thoracic and fourth lumbar vertebrae and had an overactive detrusor in urodynamic studies were included in this retrospective study. The patients were selected as they also had not responded to a combination of an anticholinergic and mirabegron and had neuropathic pain. Gabapentin treatment was added to the previous therapy. Demographics, previous treatments, chronic conditions, urodynamic findings, clinical and urodynamic responses are reported in this paper. Results We observed the response in the urodynamic studies of 11 patients (40.17%), in terms of decreased detrusor contractions, maximal detrusor pressure, and the number of the incontinence episodes. Sixteen patients did not respond to the gabapentin add-on therapy and were referred for Botulinum Toxin injections to the bladder. Conclusion Gabapentin add-on therapy can be considered as an option in neurogenic overactive detrusor patients who did not respond to the combination of anticholinergics and mirabegron. The approved usage of gabapentin for neurogenic pain justifies its usage in this area. In our selected patient group, who had not responded to the combination therapy, we observed a clinical benefit in one-third of the patients.