// stress chemistry lab

The molecules
running your body
right now.

Epinephrine, norepinephrine, and dopamine — the catecholamine trio that controls your fight-or-flight, focus, and reward systems. Explore the science interactively.

Simulate stress response → Explore molecules → Test your knowledge →
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01 — Molecules

Three chemicals.
Infinite impact.

Epi
Epinephrine
aka Adrenaline · C₉H₁₃NO₃
The emergency broadcast signal. Released from adrenal glands in seconds, it primes every system for maximum physical output — heart, lungs, muscles, eyes.
Half-life
2–3 min
Source
Adrenal medulla
HR effect
+40–60 bpm
Peak onset
< 30 sec
NE
Norepinephrine
aka Noradrenaline · C₈H₁₁NO₃
The sustained focus signal. Acts as both a hormone and neurotransmitter, tightening blood vessels, sharpening attention, and maintaining the stress response over time.
Half-life
2–3 min
Source
Locus coeruleus
BP effect
+20–30 mmHg
Receptor
α1, α2, β1
DA
Dopamine
aka DA · C₈H₁₁NO₂
The anticipation and reward molecule. Drives motivation, movement, and pleasure — and is the chemical target of nearly every addictive substance known to science.
Half-life
~1 min
Source
Substantia nigra
Mood effect
+++ motivation
Precursor
L-DOPA
02 — Deep Dive

The full story
on each molecule.

Select a catecholamine to explore its biology, pathways, clinical relevance, and what happens when levels go wrong.

The emergency
broadcast signal.

Epinephrine doesn't ask for permission. The moment your amygdala registers a threat — real or imagined — it fires a signal that reaches your adrenal glands in under a second. What follows is a full-body state change that evolution has been refining for 500 million years.

"The adrenal medulla is essentially a modified sympathetic ganglion that secretes epinephrine directly into the bloodstream — bypassing the synapse entirely."
  • Epinephrine is synthesized from norepinephrine via the enzyme PNMT (phenylethanolamine-N-methyltransferase), making NE its direct chemical precursor.
  • It acts on both α and β adrenergic receptors simultaneously — β1 speeds the heart, β2 opens airways and dilates blood vessels in muscle, α1 constricts vessels in the gut and skin.
  • The "adrenaline dump" feeling — trembling hands, tunnel vision, surge of strength — is epinephrine binding to receptors in skeletal muscle, the heart, and the eye within seconds of release.
  • Medical epinephrine (EpiPen) is chemically identical to endogenous adrenaline. In anaphylaxis, it reverses airway swelling and cardiovascular collapse within 5–15 minutes.
  • Chronic stress keeps baseline epinephrine elevated, which over time contributes to hypertension, insulin resistance, and suppressed immune function.
Biosynthesis pathway
Phenylalanine — essential amino acid from diet
Tyrosine — hydroxylation by PAH enzyme
L-DOPA — rate-limiting step via tyrosine hydroxylase
Dopamine — decarboxylation by DOPA decarboxylase
Norepinephrine — hydroxylation by DBH
Epinephrine — methylation by PNMT (adrenal medulla only)
Body system effects
Heart rate++++
Blood pressure+++
Airway dilation++++
Blood glucose+++
Gut motility−−−
When levels go wrong
Too high: Panic attacks, hypertensive crisis, pheochromocytoma (adrenal tumor causing uncontrolled epinephrine surges — headache, sweating, severe hypertension).

Too low: Inability to mount a stress response, orthostatic hypotension, extreme fatigue under physical demand. Common in adrenal insufficiency (Addison's disease).
The brain's
attention director.

Norepinephrine is the molecule that narrows your world. When it floods your brain, peripheral distractions dissolve and the threat — or the task — becomes the only thing that exists. It's the neurochemical basis of deep focus, hypervigilance, and the inability to think about anything else when you're under pressure.

"Unlike epinephrine, norepinephrine acts as both a hormone and a neurotransmitter — it simultaneously shapes your body's blood vessels and your brain's attentional spotlight."
  • The locus coeruleus — a tiny cluster of ~15,000 neurons in the brainstem — is the brain's sole supplier of norepinephrine for the cortex, hippocampus, and cerebellum. It's small but controls everything.
  • NE operates on an inverted-U curve for cognitive performance: too little causes sluggishness and inattention; too much causes anxiety and cognitive rigidity. The sweet spot is the alert, focused state.
  • Most antidepressants (SNRIs like Effexor, Cymbalta) work partly by blocking norepinephrine reuptake — keeping it active in the synapse longer and restoring the emotional floor.
  • ADHD involves dysregulation of both NE and dopamine in the prefrontal cortex. Strattera (atomoxetine) treats ADHD exclusively by targeting norepinephrine reuptake, with no dopamine effect.
  • During REM sleep, the locus coeruleus goes almost completely silent — one of the only times in your life your brain runs without norepinephrine. This is thought to be critical for emotional memory processing.
The inverted-U: NE and cognition
Optimal NE = peak cognitive performance. Deficit or excess both impair function.
Body system effects
Vasoconstriction+++++
Alertness / focus++++
Heart rate+/−
Memory consolidation+++
Pain sensitivity−−
When levels go wrong
Too high: Hypervigilance, PTSD re-experiencing, anxiety disorders, hypertensive crisis. Prazosin (α1 blocker) is used to treat PTSD nightmares by dampening NE signaling.

Too low: Depression, ADHD inattentive subtype, brain fog, poor working memory, low blood pressure. NE deficiency in the prefrontal cortex is a major contributor to treatment-resistant depression.
The molecule
of wanting.

Dopamine has a PR problem. It's been called the "pleasure chemical" for decades — but that's wrong. Dopamine isn't about pleasure. It's about anticipation, craving, and the drive to pursue. The pleasure you feel when you get something? That's mostly opioids. Dopamine is what makes you desperately want it in the first place.

"Dopamine neurons don't fire when you get the reward — they fire when you predict it's coming. Remove the reward after they've learned to expect it, and those same neurons go silent. That silence is withdrawal."
  • The mesolimbic pathway (VTA → nucleus accumbens) is the brain's core reward circuit. Every addictive drug — cocaine, alcohol, opioids, nicotine — ultimately hijacks this pathway to flood the accumbens with dopamine.
  • Dopamine encodes prediction errors: when something is better than expected, DA spikes. When it's worse than expected, DA drops below baseline. This is how the brain learns what's worth pursuing.
  • The nigrostriatal pathway (substantia nigra → striatum) controls voluntary movement. When 70–80% of these neurons die, Parkinson's motor symptoms appear — tremor, rigidity, bradykinesia.
  • Chronic overstimulation (via drugs, endless social media, junk food) causes dopamine receptor downregulation — the brain reduces its own sensitivity, requiring more stimulation to feel normal.
  • Dopamine fasting — eliminating high-dopamine stimuli for 24–48 hours — is theorized to partially restore receptor sensitivity. Evidence is preliminary but the neurochemical logic is sound.
Four major dopamine pathways
Mesolimbic
VTA → Nucleus accumbens. Reward, motivation, addiction. The "wanting" circuit.
Mesocortical
VTA → Prefrontal cortex. Working memory, attention, executive function.
Nigrostriatal
Substantia nigra → Striatum. Voluntary movement. Disrupted in Parkinson's.
Tuberoinfundibular
Hypothalamus → Pituitary. Regulates prolactin secretion.
Dopamine vs. common stimuli
Cocaine+1000%
Sex+200%
Nicotine+150%
Exercise+100%
Social media notification+50%
When levels go wrong
Too high: Psychosis, schizophrenia (excess in mesolimbic pathway), mania. Antipsychotics work by blocking D2 receptors to reduce dopamine signaling.

Too low: Anhedonia (inability to feel pleasure), depression, ADHD, Parkinson's disease, social withdrawal, loss of motivation. The absence of dopamine doesn't feel like sadness — it feels like nothing matters.
03 — Simulator

Dial up your
stress response.

Adjust the stressor intensity, duration, and type. Watch how catecholamine levels shift in real time based on physiological research data.

Epinephrine
450
pg/mL
Elevated
Norepinephrine
620
pg/mL
High
Dopamine
85
pg/mL
Normal
04 — Acute Response

0 to 60 seconds:
what actually happens.

A predator appears. Your nervous system has already reacted before your conscious mind processes it.

0 sec
Amygdala fires
Threat detected. The amygdala sends an emergency signal to the hypothalamus before conscious awareness. This happens in ~12 milliseconds.
0.1 sec
Sympathetic nervous system activates
The hypothalamus triggers the sympathetic-adrenal axis. Nerve signals race toward the adrenal glands at up to 70 m/s.
1–3 sec
Epinephrine surge
Adrenal medulla floods the bloodstream with epinephrine. Heart rate climbs. Pupils dilate. Blood redirects from gut to muscle. You feel it as a "rush."
5–15 sec
Norepinephrine sustains the response
NE narrows peripheral blood vessels, raises blood pressure, and sharpens attentional focus. You become hyperaware of your environment.
30–60 sec
Dopamine modulates the experience
Dopamine release encodes the experience and drives approach or avoidance behavior. If threat passes, dopamine contributes to the relief/reward feeling.
2–5 min
Cortisol arrives (the slow wave)
If the stressor persists, the HPA axis releases cortisol to sustain the response. This is the beginning of chronic stress territory if it doesn't resolve.
05 — Comparison

Side by side.

Property Epinephrine Norepinephrine Dopamine
Primary role Fight-or-flight activation Sustained arousal & focus Motivation & reward
Release site Adrenal medulla (80%) Nerve terminals + adrenals Substantia nigra, VTA
Heart rate Strong increase Slight decrease via reflex Dose-dependent
Blood pressure Increases Strong increase Low: increases; High: varies
Anxiety link Direct — the "panic" molecule Strong — hypervigilance Indirect — via reward dysregulation
Exercise effect 2–3x baseline increase 3–5x baseline increase Moderate increase, mood boost
Clinical use Anaphylaxis, cardiac arrest Septic shock, hypotension Parkinson's (precursor L-DOPA)
Deficiency symptoms Fatigue, poor stress response Brain fog, low energy, depression Anhedonia, Parkinson's, ADHD
06 — Knowledge Check

Think you know
your catecholamines?

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