严禁反应（英语：Stringent response）是指细菌等原核生物在缺少氨基酸的环境中生长时，细胞主动关闭蛋白质合成等一些代谢活性的反应。

氨基酸供应减少时，与氨基酸结合的tRNA数量减少而空载的tRNA增多，这种空载的tRNA是焦磷酸转移酶的激活剂，从而使得焦磷酸转移酶催化ATP转移焦磷酸基到GDP或GTP上，产生_PPG_PP（四磷酸鸟苷）和_PPPG_PP（五磷酸鸟苷），这两种物质可以使得某些基因的表达被关闭。

The stringent response, also called stringent control, is a stress response of bacteria and plant chloroplasts in reaction to amino-acid starvation, fatty acid limitation, iron limitation, heat shock and other stress conditions. The stringent response is signaled by the alarmone (p)ppGpp, and modulates transcription of up to 1/3 of all genes in the cell. This in turn causes the cell to divert resources away from growth and division and toward amino acid synthesis in order to promote survival until nutrient conditions improve.