Ironically, school is often the adrenaline junkie's first "drug dealer." At some point, most students procrastinate an assignment until the last minute, at which point, the fear of not getting it done triggers an adrenaline surge, which fuels getting it done, and it can feel good to be pumped up. When, thanks to grade inflation, they get a good grade, school thus has taught them that using adrenaline to get stuff done is okay.
Similarly, a student gets an adrenaline hit when making a snarky comment in class but teachers rarely impose serious consequences, so again the school contributes to a student becoming an adrenaline junkie.
Of course, school is far from the only cause of adrenaline addiction. After a teen gets comfortable behind the wheel, s/he may push the speed and safety limit, not so much to get somewhere a bit faster, but for the adrenaline hit. In dating, a person can get a rush from too quickly having sex, unsafe sex, or edgy sex. Then there are dangerous sports such as motorcycle racing, rock climbing, and parachute jumping.
Lying, stealing, gambling, and substance abuse also yield an adrenaline rush. So can picking a fight: a physical one or an argument about a controversial subject such as politics or race. Usually, that yields more adrenaline than benefit.
Perhaps more subtle, adrenaline can be triggered by catastrophizing everything from an unusual bodily sensation to the impact of a Trump presidency or of "comprehensive immigration reform."
Of course, those behaviors impose strong negatives. Apart from problems with the behaviors themselves, excessive stress is unhealthy, triggering both adrenaline and cortisol secretion.
The more a person does such behaviors, the more s/he feels life is boring without the adrenaline hit, and thus is made the adrenaline junkie, seeking ever more and ever higher highs.
Adrenaline addiction's upside
In fairness, adrenaline addiction has upsides. It can fuel people to accomplish more than they otherwise would. For example, many adrenaline-addicted people get a constant hit of adrenaline by always hurrying, cramming in as much activity as possible. True, they may be more error-prone but, in my experience with such "Type A" clients—and to be honest, me—most of this group, net, does get more done—although not if it causes a heart attack.
Managing your adrenaline addiction
First, decide if and how you'd like to alter your adrenaline flow. If you feel you've been too phlegmatic in your life, you might play an adrenaline-triggering game or two.
More likely, you'll want to reduce your adrenaline flow. It needn't be all or nothing. Focus on one or two areas in which your adrenaline addiction particularly isn't of benefit. For example, I gain almost nothing by driving too fast and lose what should be a relaxing part of my day while risking a speeding ticket.
Some people also believe that meditation, yoga, or deep breathing help. Alas, my clients and I have generally found that the relaxing effect of those activities only minimally transfers into daily life.
As with most behaviors, by the time you're old enough to read Psychology Today, it may well be difficult to dramatically change your personality. Just as you can fine-tune a TV but not turn a black-and-white TV into a color one, if you tend toward adrenaline addiction, you might want to just focus on fine-tuning.
My eighth book is The Best of Marty Nemko.