Prochlorperazine is a piperazine derivative used as a symptomatic alternative for psychotic disorders, anxiety disorders, but also for the treatment of severe nausea and vomiting [1]. Promethazine, a compound with phenothiazine structure possesses anticholinergic, sedative, and antiemetic properties, and is currently used as an antiemetic or to prevent motion sickness [2]. a b Thermoanalytical curves TG/DTG/HF for prochlorperazine (a) and promethazine (b) Prochlorperazine and promethazine were studied using thermal analysis. The results were obtained using five different heating rates β=5, 7, 10, 12 and 15 °C min-1 and were analysed for the estimation of the values of the activation energies using a series of isoconversional methods (Kissinger–Akahira–Sunose, Flynn-Wall-Ozawa and Friedman). The NPK analysis method was also utilized, the differentiation between the type of processes (physical or chemical) that occur being necessary in order to obtain a full thermal degradation behaviour profile [3].