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Colloquially, an adrenaline junkie is somebody who appears to be addicted to adrenaline. Adrenaline in this case comes from an endogenous source (i.e. the adrenal gland) and does not imply the use of exogenous adrenaline (e.g. injection).
Edward Cullen often gets adrenaline rushes.
The term came into use in 1993. Originally, it was used to describe argumentative people who deliberately (consciously or unconsciously) find excuses to get an adrenaline fix. This mode of receiving a fix is deemed just as addictive as a recreational drug (such as heroin, hence the term "junkie"), but can be considered more harmful if it involves other people. The phrase adrenaline junkie was used in the 1991 movie Point Break to describe the "Ex-Presidents." Adrenaline redirects here. ... Look up Endogenous in Wiktionary, the free dictionary. ... In mammals, the adrenal glands (also known as suprarenal glands) are the triangle-shaped endocrine glands that sit on top of the kidneys; their name indicates that position (ad-, near or at + -renes, kidneys). They are chiefly responsible for regulating the stress response through the synthesis of corticosteroids and catecholamines... Exogenous (or exogeneous) (from the Greek words exo and gen, meaning outside and production) refers to an action or object coming from outside a system. ... Heroin (INN: diacetylmorphine, BAN: diamorphine) is a semi-synthetic opioid synthesized from morphine, a derivative of the opium poppy. ... Point Break is a 1991 action film starring Keanu Reeves and Patrick Swayze, and directed by Kathryn Bigelow. ...

Pharmacokinetics

Although the term "adrenaline junkie" is normally used facetiously and without any genuine implication of addiction, there may be an element of truth to the description. Psychological addiction to an "adrenaline rush" has been reported numerous times.^{[citation needed]} This article is about the concept of addiction. ...

An adrenaline rush is usually accompanied by an increase in endorphin activity. Endorphins are responsible for feelings of well being, as well as pain relief. Due to synaptic plasticity, increased endorphin activity creates an increase in endorphin receptor sites, which in turn can create a stronger desire for endorphins. Synaptic plasticity and receptor site proliferation are widely believed to be the mechanisms by which chemical addictions are developed. For other uses, see Endorphin (disambiguation). ... In neuroscience, synaptic plasticity is the ability of the connection, or synapse, between two neurons to change in strength. ... In biochemistry, a receptor is a protein on the cell membrane or within the cytoplasm or cell nucleus that binds to a specific molecule (a ligand), such as a neurotransmitter, hormone, or other substance, and initiates the cellular response to the ligand. ...

However, the same can be said for any endorphin-stimulating activity, whether laughter, physical exertion, sexual intercourse, artistic expression or religious experience. Although synaptic plasticity may be responsible for chemical addictions, it is also believed to be involved in reinforcement, the mechanism by which animals learn to differentiate what is desirable from what is undesirable. Seen in this context, chemical addiction could simply be seen as an aberrant form of plasticity. For the construction materials reinforcement, see Rebar. ...

Although the effects of adrenaline are largely positive, increasing cardiovascular activity and oxygenation, extended or chronic adrenal stimulation can eventually lead to high blood pressure, heart disease, and other stress-related diseases. The circulatory system or cardiovascular system is the organ system which circulates blood around the body of most animals. ...