Non-steroid anti-inflammatory drugs are commonly used both in medicine and veterinary medicine. The aim of the paper was to determine the effect of diclofenac calcium, the active ingredient of a medicine called diclofenac, on the development rate and survivorship of the fly Lucilia sericata (Meigen, 1826) (Diptera: Calliphoridae). Diclofenac was used at three concentrations: it was mixed with pork meat in proportions 25 mg of the drug 23 g of meat (dose 1), 50 mg/23 g (dose 2) and 75 mg/23 g (dose 3). To compare the results, a control sample was used (23 g of drug-free meat). All diclofenac calcium doses delayed the development of L. sericata. Moreover, all the drug doses (25 mg, 50 mg, 75 mg) resulted in body weight loss of L. sericata larvae. Finally, all the drug doses increased the mortality of L. sericata. The findings indicate that forensic entomology and forensic veterinary analyses involving L. sericata need to take into account a potential factor modifying the fly natural life cycle – the presence of diclofenac calcium in the body. A reduction of the body mass and a longer, than normal developmental cycle of L. sericata may be of significant in correctly determining the time of death of humans or animals in cases of diclofenac application.