Some adventure for glory, some for treasure. Some are even there for an ideal or personal improvement. You are none of these things. The adrenaline junkie adventures for one reason and one reason alone- the thrill of it all. Adrenaline junkies are often reckless, throwing themselves heedlessly into danger in the midst of battle. That danger, fear, and most importantly, excitement is an adrenaline junkie's bread and butter, where they are most effective and most comfortable. 

Adrenaline Rush

Beginning when you choose this archetype at 3rd level, you have begun to harness your body's adrenaline for use in combat. While your health is below half of your hit point maximum, you gain the following effects.

+10' walking speed

-advantage on dexterity saving throws

-You critically hit on a 19 or 20

Always Ready

Beginning at level 7, your adrenaline allows you to react faster than a normal person, whether it be to an enemy approaching or a friend being hurt. You may add your Constitution modifier when you roll initiative. Also, when an ally would be hit by a weapon or spell attack, you may use your reaction to move up to your speed towards them. If you reach their space, you may swap positions with them and take the damage instead. Damage taken this way cannot be reduced or ignored. 

Fortune Favors the Bold

Starting at level 10, you have the luck of a fool and talent to match. When a creature hits you with a weapon attack, you may use your reaction to instead have it miss you. You gain advantage on all attacks against the creature until the end of your next turn.

Enhanced Adrenaline Rush

Beginning at level 15, when you have under one quarter of your health you gain a bonus to your attack and damage rolls equal to your Constitution modifier.

Fueled by Pain

At 18th level, you have achieved mastery of your adrenaline, even as it pushes you to dangerous extremes. You have gained the ability to pump harmful amounts of adrenaline into yourself to produce powerful effects. As a bonus action, you can deal damage to yourself equal to twice your level in order to recharge a use of your action surge feature. This ability cannot bring your current charges of action surge to greater than two.