By Dr. Mercola

Avid exercisers often enjoy a euphoric feeling after their workouts. Sometimes called a "runner's high," this notable post-workout boost in happiness and energy levels is what keeps many devoted exercisers coming back for more.

The feel-good vibes are typically attributed to endorphins, which are neurochemicals produced in your brain's hypothalamus and pituitary gland. These natural painkillers are similar in structure to the drug morphine and activate opioid receptors in your brain to help minimize pain.

Endorphins are linked to your body's reward circuits as well and are associated with other feel-good activities like maternal behavior, eating and drinking or having sex.¹

Endorphins in your blood also increase in response to pain and stress, such as exercise, and it's long been suggested that these endorphins help people feel good after their workouts. There's even a term, "endorphin junkie," often used by gym rats who are "addicted" to the exercise "high." There's just one problem.

Endorphins Can't Cross Your Blood-Brain Barrier

The idea that endorphins cause the runner's high has been in circulation for decades. Dr. J. Kip Matthews, a sport and exercise psychologist, told CNN:²

"Long-distance running was quite popular in the mid-1970s around the same time that endorphins were discovered. Anecdotally, there were a lot of reports of the so-called 'runner's high.'

… By suppressing the experience of pain, a number of researchers put forth the idea that endorphins could be the source of this euphoric feeling after intense exercise."

However, as CNN reported, research has shown that endorphin levels might not increase in your body until you've exercised for a full hour.³

So why you can still feel euphoric after a very short, intense workout like high-intensity interval training (HIIT)? Some research suggests endorphins are only produced during anaerobic exertion, such as HIIT or intense weight training (and not during typical aerobic exertion unless you exercise for about an hour).⁴

This still doesn't explain the full picture, however, as most related studies have measured endorphin levels in your blood during exercise. This isn't indicative of the endorphin levels in your brain, because endorphins can't cross your blood-brain barrier.⁵

So while exercise may increase blood levels of endorphins, it's the endorphins in your brain that would make you feel good. And research hasn't proven that exercise increases brain levels of endorphins.

What does increase in your brain following exercise is a neurotransmitter called anandamide, sometimes known as the bliss compound.

'Bliss Compound' May Be Involved in the Runner's High

Anandamide is a neurotransmitter and endocannabinoid produced in your brain that temporarily blocks feelings of pain and depression. It's a derivative of the Sanskrit word "bliss," and a deficiency is associated with increased anxiety and stress.⁶

Anandamide is actually found in chocolate too and is thought to be one reason why eating chocolate may give you a boost in mood (chocolate also contains other chemicals that prolong the "feel-good" aspects of anandamide).

In relation to exercise, however, anandamide levels are known to increase during and following exercise. Anandamide may also be involved in increasing a protein called Brain Derived Neurotrophic Factor (BDNF).

In your brain, BDNF not only preserves existing brain cells,⁷ it also activates brain stem cells to convert into new neurons and effectively makes your brain grow larger. Research published in the journal Psychoneuroendocrinology concluded:⁸

" … [A]cute exercise represents a physiological stressor able to increase peripheral levels of anandamide and that BDNF might be a mechanism by which anandamide influences the neuroplastic and antidepressant effects of exercise."

A recent animal study similarly found that anandamide might be responsible for producing a "runner's high" in mice. According to that study:⁹

"Exercise is rewarding, and long-distance runners have described a runner's high as a sudden pleasant feeling of euphoria, anxiolysis [anxiety relief], sedation, and analgesia [pain relief]. A popular belief has been that endogenous endorphins mediate these beneficial effects.

However, running exercise increases blood levels of both β-endorphin (an opioid) and anandamide (an endocannabinoid) … we … demonstrate that the endocannabinoid system is crucial for two main aspects of a runner's high."

Exercise Also Boosts Serotonin, Norepinephrine and Your Body's Stress Response

Exercise has undeniable effects on your mood, with anxiety reduction key among them.

A study by Princeton University researchers revealed that exercising creates new, excitable neurons along with new neurons designed to release the GABA neurotransmitter, which inhibits excessive neuronal firing, helping to induce a natural state of calm.¹⁰

Commonly prescribed anti-anxiety drugs like Ativan, Xanax and Valium actually exert a calming effect in this same manner, by boosting the action of GABA. The mood-boosting benefits of exercise occur both immediately after a workout and continue on in the long term.

In addition to the creation of new neurons, including those that release the calming neurotransmitter GABA, exercise boosts levels of potent brain chemicals like serotonin, dopamine, and norepinephrine.

This may help buffer some of the effects of stress. Matthews, the exercise physiologist, continued to CNN:¹¹

"What appears to be happening is that exercise affords the body an opportunity to practice responding to stress, streamlining the communication between the systems involved in the stress response …

The less active we become, the more challenged we are in dealing with stress."

Exercise Is Scientifically Proven to Benefit Symptoms of Depression

Exercise is one of the most effective prevention and treatment strategies for depression. One study found that 30-minute aerobic workouts done three to five times a week cut depressive symptoms by 50 percent in young adults.¹² A meta-analysis published in the Cochrane Database of Systematic Reviews even found that exercise is moderately more effective than a control intervention for reducing symptoms of depression.¹³

A Duke University team also studied three groups that tried exercise only, exercise plus drugs, and drugs only to see what treatment best treated depression. They found that, 10 months later, it was the exercise-only group that was most successful in maintaining wellness and avoiding a depression relapse. James Gordon, M.D., a world-renowned expert in using mind-body medicine to heal depression, stated in our 2008 interview:

"What we're finding in the research on physical exercise is the physical exercise is at least as good as antidepressants for helping people who are depressed. And that's even better for older people, very interesting, even more important for older people. And physical exercise changes the level of serotonin in your brain. It changes, increases their levels of 'feel good' hormones, the endorphins.

And also — and these are amazing studies — it can increase the number of cells in your brain, in the region of the brain, called the hippocampus … it's very important because sometimes in depression there are fewer of those cells in the hippocampus, but you can actually change your brain with exercise. So it's got to be part of everybody's treatment, everybody's plan."

Exercise Activates Pleasant-Activated Feelings

A study on undergraduate students found those who were more physically active overall had higher pleasant-activated feelings than people who were less physically active.¹⁴ Pleasant-activated feelings include excitement and enthusiasm, which some might say would be the opposite of depression.

Further, on days when the students engaged in more physical activity than normal, they reported higher levels of these positive feelings as well. Researcher Amanda Hyde told EurekAlert:¹⁵

"Our results suggest that not only are there chronic benefits of physical activity, but there are discrete benefits as well … Doing more exercise than you typically do can give you a burst of pleasant-activated feelings. So today, if you want a boost, go do some moderate-to-vigorous intensity exercise."

Rather than viewing exercise as a medical tool to lose weight, prevent disease, and live longer — all benefits that occur in the future — try viewing exercise as a daily tool to immediately enhance your frame of mind, reduce stress and feel happier.

Let Happiness Be Your Motivation to Exercise

A common reason people fail in their exercise goals is feeling lack of a payoff. In other words, while exercise might help you to lose weight in a few weeks or prevent a heart attack a few years down the road, there may appear to be no immediate and noticeable reward to keep you motivated.

Or is there? Research shows that while many people started an exercise program to lose weight and improve their appearance, they continued to exercise because of the benefits to their well-being.¹⁶ Once people recognized this connection to their emotional health, they continued to work out because it made them feel good mentally, and this is a benefit that occurs immediately after exercise (as well as, for some, during).

Dr. Michelle Segar, author of the book "No Sweat: How the Simple Science of Motivation Can Bring You a Lifetime of Fitness," explained to the New York Times that harnessing this happy feeling can compel you to stick with your exercise program in the long term:¹⁷

"It [Exercise] has to be portrayed as a compelling behavior that can benefit us today ... People who say they exercise for its benefits to quality of life exercise more over the course of a year than those who say they value exercise for its health benefits.

…  Immediate rewards are more motivating than distant ones ... Feeling happy and less stressed is more motivating than not getting heart disease or cancer, maybe, someday in the future. …  Physical activity is an elixir of life, but we're not teaching people that. We're telling them it's a pill to take or a punishment for bad numbers on the scale. Sustaining physical activity is a motivational and emotional issue, not a medical one."