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The Brain's Delicate Chemistry

The difference between a healthy brain and an unhealthy one is not wide.

Jacob Lund/Shutterstock
Source: Jacob Lund/Shutterstock

Humans are made up of chemicals. Tiny molecules communicate with other tiny molecules that dictate our mood, our neuroses, and even our personalities. When these chemicals go awry, our brains change and—unfortunately—so do we.

Runner’s High

Chemicals aren’t going awry when an athlete experiences “runner’s high,” or a burst of euphoria during (or after) a particularly intense bout of exercise. In fact, scientists suspect that this pleasant, exercise-induced feeling poses an evolutionary advantage, allowing humans to run away from predators or hunt prey without growing too exhausted. Recent research has indicated that dogs—like humans—also experience a form of runner’s high, likely because their survival also depends on running long distances. (In contrast, ferrets do not experience runner’s high, likely because they spend most of the day sleeping.)

Until recently, scientists had suspected that runner’s high had to do with heightened levels of endorphins, or neuropeptides that act as the body’s internal stash of painkillers. They believed this because after strenuous exercise, athletes had increased levels of endorphins in their bloodstream along with an increased tolerance for pain. More recent evidence, however, indicates that endorphins are too large to travel between the blood stream and the brain. Instead, scientists have implicated endocannabinoids in that euphoric, post-exercise glow.

(A side note: Endorphins shouldn’t be completely discounted just yet—research has indicated that naltrexone, a medication that blocks the effects of endorphins on the brain, can effectively eliminate runner’s high. Chances are the brain uses both endorphins and endocannabinoids to relieve pain and create euphoria during exercise, but the mechanisms are unclear.)

Like all good things, however, the bliss that comes from runner’s high can be abused. Over-exercising, or pushing your body beyond its limits, can be an excellent way to achieve runner’s high—and to irreparably damage your muscles.


Self-harm—or non-suicidal self-injury—is when a person intentionally injures himself or herself. Individuals who self-harm may cut themselves, burn themselves, pick at their skin, or use another method to make themselves bleed. People often describe self-harm as cathartic, sobering, or even euphoric.


When people are injured, their body releases natural chemicals such as endorphins and endocannabinoids. People who self-harm may be intentionally injuring themselves so that they can receive these soothing, pain-killing chemicals and ease their mental suffering.

But if self-harm releases a flood of calming chemicals in the brain, why doesn’t everyone do it? Researchers suspect that individuals who self-harm have naturally lower levels of endogenous opioids (endorphins) than the rest of the population. Therefore, to compensate for their lack of “happy chemicals,” these individuals may turn to self-harm in an effort to feel normal.

Like runner’s high, the mechanisms associated with self-harm have an evolutionary advantage. After all, if someone punches you in the face, you don’t want to collapse—you want to have the energy to run or fight back. Continuing onward despite injury is as vital to our species’ survival as reproduction.

Sex addiction

Most of us enjoy sex. It floods the brain with pleasant chemicals and makes us feel happy and healthy. Some individuals, however, become so obsessed with sex that it interferes with their lives. These are individuals with sex addiction, or compulsive sexual behavior.

Scientists still aren’t sure whether we can consider sex addiction a mental illness. In the latest version of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), sex addiction was conspicuously absent. Regardless of classification, though, there are individuals who live with compulsive sexual thoughts and behaviors. A recent study from the University of Cambridge found that individuals who struggle with compulsive sexual behavior demonstrated brain activity not unlike what scientists have observed in drug addicts.

Sex addiction also appears to be mediated—at least in part—by endorphins and other endogenous opioids. Naltrexone, a chemical known for blocking the euphoric effects of opioids, has shown to mitigate symptoms in adolescents with compulsive sexual behavior. In a case study by the Mayo Clinic, clinicians found that they could virtually cure a patient’s addiction to Internet pornography by targeting his endogenous opioids through naltrexone.

In other words, for people with compulsive sex addiction, the flood of brain chemicals that most of us find pleasant is actually harmful—and only by blocking these chemicals can those individuals lead normal lives.


So what do sex addiction, self-harm, and runner’s high all have in common? All involve chemicals designed to help us survive—whether by running long distances, persevering despite pain, or passing down our genes—and all can become dangerous given the right (or wrong) circumstances.

Since our brains are composed of chemicals that may one day go awry, it’s a good idea to take care of ourselves in the meantime. Go to bed early. Eat a healthy diet. Exercise, but not so much that you get hooked on it. The difference between a healthy brain and an unhealthy one is smaller than you realize.

Contributed by Courtney Lopresti, M.S. Neuroscience