Endorphins during any physical activity are hormones that are initially released to numb the pain caused by exercise. Although this is their main purpose in our bodies during exercise, they also have another beneficial side effect, making us happier. When I run, there are sometimes moments when I am so overwhelmed with happiness that I feel like I could run forever. I feel like nothing can harm me during a race, and everything in the world I'm holding on to my shoulders becomes a little lighter. The happiness doesn't stop when I stop running either, my mood stays positive for a considerable amount of time. As Gillen mentions in The Hidden Mechanics of Exercise: Molecules That Move us, "And while exercise activates some of the same pathways as drugs like marijuana and heroin, it prevents (or even counteracts) some of their effects." harmful”. Gillen is trying to express in this statement that exercise gives an effect comparable to that of many medications, except that the side effects do not harm us, but actually help.