During times of extreme stress, fear or anxiety, the human brain will often signal the release of a powerful stimulating chemical known as epinephrine or adrenaline. This sudden flood of adrenaline is designed to give the body a boost of strength and awareness during a "fight or flight" situation. Once the immediate danger has passed, the average person's body will slowly ramp back down to normal levels and the additional adrenaline will be absorbed and eliminated. Because this rush of adrenaline can bring with it some of the same satisfying effects as other drugs, however, some people can actually become addicted to the natural "high" they experienced during the event. A person who craves the release of adrenaline and is willing to go to extreme measures to get it is commonly referred to as a adrenaline junkie.

A typical adrenaline junkie is often associated with the world of extreme sports. Participants in such dangerous sports as auto racing, skydiving and bungee jumping face the real possibility of serious injury or death, but these sports also provoke the desired fight-or-flight stress response an adrenaline junkie craves. Whenever an extreme skydiver or base jumper jumps out of an airplane or runs off the edge of a cliff, he or she triggers a rush of natural hormones and chemicals which give him or her a sensation of being fully alive. An adrenaline junkie often feels extremely depressed or unmotivated in his or her daily life until the opportunity to do something death-defying arrives. Essentially, a true adrenaline junkie lives his or her life at either level 10 or level 0.

Extreme sports are not the only arena in which an adrenaline junkie thrives, however. A person with a thrill-seeking personality often seeks out employment which involves a high level of risk or drama. An adrenaline junkie may take on jobs which require extraordinary courage or risk-taking, such as a firefighter, police officer, or professional military soldier. The stress and thrill of rescuing a trapped passenger from a burning car or chasing down a suspected criminal would provide the same kind of rush as an extreme sport for an adrenaline junkie. For an adrenaline junkie, taking on a dangerous assignment or volunteering for hazardous duties allows him or her to experience life to its fullest.

One concern many people have for an adrenaline junkie's overall well-being is his or her constant need for danger and drama. Friends and family of a true adrenaline junkie often find it difficult to maintain a normal relationship with him or her. An adrenaline junkie often provokes conflict with others simply for the rush associated with the fight. Others who fail to keep up with an adrenaline junkie's edgy and anarchic lifestyle may find themselves marginalized or abandoned. An adrenaline junkie's lows are often as deep as his or her highs, which can make it extremely difficult for him or her to maintain a normal, functional lifestyle. If an adrenaline junkie is not killed or seriously injured in active pursuit of his or her next "high", then he or she may eventually burn out from the effects of a reckless lifestyle.