On all the worms, mianserin had some surprising effects on the worms’ gene expression. Think of genes as a long line of light switches that can be turned off or on. Typically, throughout an organism’s life, one or two genes might get switched on or off at a time. When the roundworms were treated with mianserin, the drug affected a group of switches that affect all the lights in one room (or function of the body), but instead of flipping them all off, or freezing them in place, the drug caused each one to switch position. The expression of the “off” genes in that group was turned on, and the “on” genes were turned off. The most profound effects on the worms’ genetic expression were in those treated with mianserin earliest.