Cigarette butts (CBs) have only recently begun to be considered environmentally harmful waste. CBs are common waste in the environment, that can cause air, soil, and water pollution and pose a threat to the living. CBs should be treated as toxic and hazardous waste due to its slow decomposition and accumulation of many toxic substances. There is a lack of research on the adaptation of CBs to the environment and what impact they have on vegetation. Therefore, the present work aimed to understand the toxicity of smoked CBs. Leachates of various concentrations were assessed with ecotoxicological tests. The effect of CBs on germination and development of plants at their early stage of growth was determined. Seeds of Sinapis alba L. and Hordeum vulgare L. were used in the CBs toxicity test. Two-way ANOVA was conducted to compare the main effects on plants. From the results, it is evident that low concentrations of toxic substances contained in CBs have a positive effect on plants; however, Hordeum vulgare L. expresses higher toxic resistance than Sinapis alba L. It has been proven that high concentrations of CBs in a water solution have negative effects on seed germination and radical growth. This research shows that varied plant species can cope with different levels of contamination by hazardous elements. CBs are an important source of contamination for the environment and the hazardous elements that are released from them when inappropriately disposed of can impair the development of plants and accumulate in them.