Abstract Acetaminophen and caffeine, popular therapeutic substances used to relieve pain or alleviate the symptoms of cold. The aims of the study were the comparison of granules, in terms of dissolution rate and moreover the development of spectrophotometric method to the simultaneous determination of both active pharmaceutical ingredients (APIs) in granules. The granules were tested by two pharmacopoeial methods of dissolution for solid dosage forms, and the dissolution profiles for each formulation were compared. A method of simultaneous determination of two medicinal substances by the double calibration method using derivative spectrophotometry was used. Considering the dissolution process carried out in the paddle apparatus, it was shown that more than 80% of acetaminophen and caffeine were released from each of the preparations in a clearly shorter time than 10 minutes. Carrying out the basket test, substances dissolved gradually, much slower than in the paddle method. The time required to release 80% of both active substances from majority of tested preparations was from 30 to 45 minutes. Application of the first derivative spectrophotometric method allows simultaneous determination of acetaminophen and caffeine in the mixture, without the need to separate them first.