Exercise produces a less extreme spike in dopamine, endorphins, and other feel-good chemicals. Drugs like cocaine or heroin wallop the system, but exercise merely stimulates it, leading to very different long-term adaptations. The brain reacts to regular exercise not by suppressing activity in the reward system, but by facilitating it. In direct contrast to drugs of abuse, exercise leads to higher circulating levels of dopamine and more available dopamine receptors. Instead of annihilating your capacity for pleasure, exercise expands it.
