Background Hyoscine butyl bromide is used as an antispasmodic in treating peptic ulcer, gastritis and various disorders of the gastrointestinal tract which are characterized by spam. It has also found employment for the relief of spasmodic conditions of the bile duct and urinary tract and for the treatment of dysmenorrhea. Objective In this study, the application of silver nanoparticles (Ag NPs) as a colourimetric probe for the fast, selective and simple determination of hyoscine butyl bromide was described. Methods The proposed method was based on the Ag NPs aggregation induced by their interaction with the cited drug. This interaction produced a colour change from yellow to colourless measured at 405 nm. Results The method linear concentration range was 0.10–50.0 µg/mL with a correlation equation (Y = 0.0132 X + 0.3174), correlation coefficient of 0.9981 and quantification limits of 0.091 µg/mL. A thorough investigation was done to validate the method's analytical performance, and the findings were satisfactory. With great accuracy and precision, this approach was used to identify the medication in pharmaceutical tablet samples with recovery percentages ranging from 96.20 to 98.10%. Conclusion Since there are no critical reaction conditions or solvent extraction involved in the described method, it is distinguished by its simplicity. The results were quite consistent with those attained using the approved standard method. Highlights Simple, fast, and sensitive colorimetric probe developed for determination of hyoscine butyl bromide in pharmaceutical formulations.