The 3^rd-instar Culex pipiens molestus Forskal larvae were used in this study to evaluate the toxicity of different concentrations of some drugs (niclosamide, isoniazid, piperazine, sulfasalazine, and 4-amino antipyrine). The mosquito mortality percentages were calculated using a gradient concentration of the examined medicines to estimate the acute toxicity testing. A concentration of 15 ppm of niclosamide on the 4th day of the experiment had a deadly impact on a mosquito's third instar larvae, resulting in a 100% death rate. The LC₅₀ value of the niclosamide solution was found to be 23.11.  On the 2^nd day of treatment, however, 140 ppm of isoniazid resulted in 100% larval mortality. The LC₅₀ value of the isoniazid solution was found to be 206.16. Practically all of the treated larvae were killed by the 300 ppm dosage of piperazine on the 3^rd day of the treatment. The LC₅₀ value of the piperazine solution was found to be 504.38. A concentration of 400 ppm of sulfasalazine on the 5^th day of the experiment had a deadly impact resulting in a 100% death rate on mosquito's larvae.  The LC₅₀ value of the sulfasalazine solution was found to be 626.59. During the 3^rd day of the study, a concentration of 2000 ppm of 4-aminoantipyrine caused 100% fatality in the larvae. The LC₅₀ value of the 4-aminoantipyrine solution was found to be 3656.57. The effect of drug solutions as an inhibitor of egg-laying was that the concentrations used to kill third-instar larvae of mosquitoes had an effect of preventing egg-laying by 100% at all concentrations except for the niclosamide solution, which gave an egg-laying prevention percentage of 54.2, 43.4, 26.0, and 12.4 for concentrations 15, 12, 9, and 7 ppm, respectively. The concentrations used in the experiment to kill the third instar of mosquitoes were reduced to reach the concentrations at which female mosquitoes could lay eggs.