Neurotransmitters are the brain chemicals that communicate information throughout your brain and body. They pass signals between nerve cells, called neurons. The brain will use neurotransmitters to control your heartbeats, your breathing, and your digestion. Indirectly through the endorine system it will also control your mood, sleep, concentration, weight. When out of balance, the neurotransmitters can cause adverse symptoms. Neurotransmitter levels can become depleted, and estimated 86% of Americans live with suboptimal neurotransmitter levels. Stress, poor diet, neurotoxins, genetic predisposition, drugs (prescription and recreational), alcohol and caffeine use will cause neurotransmitter levels to go out of optimal range. We recognize two types of neurotransmitters Excitatory and Inhibitory. Excitatory neurotransmitters stimulate and Inhibitory calm the brain. Inhibitory neurotransmitters tend to balance your mood and when the excitatory neurotransmitters are too high you will tend toward imbalance.

Inhibitory Neurotransmitters

Serotonin is an inhibitory neurotransmitter that is required to balance any excessive excitatory (stimulating) neurotransmitters firing in the brain and to balance your moods. Any stimulant medications or caffeine can cause a depletion of serotonin over time. Serotonin regulates many processes including carbohydrate cravings, sleep cycle, pain control and appropriate digestion. Low serotonin levels are associated with depressed immune system.

GABA is an inhibitory neurotransmitter that is often referred to as natures chill-pill . When GABA is out of range (too high or too low), it suggests that an excitatory neurotransmitter is firing too often in the brain. GABA will be sent out to attempt to balance this stimulating over-firing

Dopamine is a special case, it can be both excitatory and inhibitory. Dopamine will lift depression, improve your focus.

Excitatory Neurotransmitters

Dopamine improves your ability to focus your attention. When dopamine is either high or low you will experience focus issues – not remembering where you put the remote control, forgetting what you just read, leading you to daydreaming and not being able to stay on task. Dopamine is responsible for your drive and desire to get things done, your motivation. Stimulants including medications for ADD/ADHD and caffeine cause dopamine to be pushed into the synapse so that focus is improved. Unfortunately, stimulating dopamine consistently can cause a depletion of dopamine over time.

Norepinephrine is an excitatory neurotransmitter that is responsible for stimulatory processes in the body. Norepinephrine also helps to make epinephrine. It can cause anxiety when high and Mood Lowering effects when low. Low levels of norepinephrine will cause Low Energy, Decreased Focus and Sleep Cycle Disturbances.

Epinephrine is associated with stress. Epinephrine will be elevated when you are not able to focus. Long term stress or sleep deprivation will cause epinephrine levels to be depleted (low). Epinephrine regulates your heart rate and blood pressure.

Histamine is an excitatory neurotransmitter associated with allergy and inflammation. It is mostly produced in the gut. Elevated histamine will trigger excess stimulation of catecholamines (dopamine, norepinephrine and epinephrine).

Definition of Neurotransmitter

A chemical or peptide substance that transmits nerve impulses across synapses (space between two neurons), that effect motor coordination, mood, behavior, and other physiological activities. Psychotropic medications alter the levels of specific neurotransmitters in the synapse or alter neurotransmission itself. For example SSRIs act by blocking reuptake of the neurotransmitter serotonin from the synapse, increasing the ability of serotonin to bind to serotonin receptors. An example of altering neurotransmission can be seen in antipsychotic medications, these medications antagonize (block) dopamine receptors in the brain, making it near impossible for dopamine transmission to occur.

Neurotransmitter Physiologic Action Effect of Excess Effect of Deficit
Dopamine (catecholamine)

  • Precursor is the amino acid tyrosine
  • Four major tracts in the brain: mesocortical, mesolimbic, nigrostriatal, tuberoinfundibular
  • Two major receptor groups: D1-D5 and D2, 3, 4
  • Thinking
  • Decision-making
  • Respond with reward-seeking behaviors; i.e., the gusto neurotransmitter
  • Fine muscle movements
  • Integration of thoughts and emotions
  • Stimulates the hypothalamus to release hormones affecting thyroid, adrenal, and sex hormones
  • Mild: Helps with creativity
  • Assist with problem-solving
  • Able to generalize situations
  • Good spatial ability Severe: Disorganized thoughts
  • Loose associations
  • Disabling compulsions
  • Tics
  • Stereotypic behaviors
  • Mild: Poor impulse control
  • Poor spatial ability
  • Inability to have abstract thinking
  • Severe: Parkinson’s disease
  • Endocrine changes
  • Movement disorders
Norepinephrine (catecholamine)

  • Only 1% of all brain neurotransmitter volume
  • Precursor is dopamine
  • Measured in the urine as MHPG
  • Major receptor groups are -1, -2, and -1, -2
  • Alertness
  • Ability to focus attention
  • Ability to be oriented
  • Primes nervous system for fight or flight
  • Arouses senses
  • Ability to learn
  • Increases memory
  • Awareness
  • Stimulates sympathetic nervous system
  • Anxious
  • Hyperalert
  • Paranoid
  • Loss of appetite
  • Dull
  • Low energy
  • Depression
Epinephrine (catecholamine)

  • Precursor is norepinephrine
  • Released by the adrenal medulla in response to stress
  • Overrides inhibitory and other neurotransmitters to provide immediate strength and single-focused concentration
  • Released by the lower brainstem and directly stimulates the hypothalamus to release hormones
  • Inhibits firing in the locus coeruleus
  • Acts on -1, -2, -1, and -2 receptors predominate in the brain with -1 the most dominant in the cortex and -2 in the cerebellum to provide rapid response to perceived threats
  • Overstimulation of all mental and physical functions
  • Cardiac arrest
  • Manic behaviors
  • Paranoia
  • Dull
  • Low energy
  • Depression
  • Muscle weakness
Serotonin (indoleamine)

  • Helps to balance norepinephrine/dopamine through inverse relationship in adrenergic nervous system
  • Precursor is the amino acid tryptophan
  • Measured in urine as 5-HIAA
  • 24 major receptor groups include 1, 2, 3, 4, 5, 6 with subgroups under each major group
  • Inhibits activity and behavior
  • Increases sleep time
  • Reduces aggression, play, sexual, and eating activity
  • Temperature regulation
  • Sleep cycle
  • Pain perception
  • Regulates mood states
  • Precursor to melatonin, which plays a role in circadian rhythms, some depressions, light-dark cycles, jet lag, female reproductive cycle, seasonal skin pigment changes
  • Sedation
  • If greatly increased, the metabolites may lead to hallucinations
  • Irritability
  • Hostility
  • Depression
  • Sleep disturbance

  • Precursor is the amino acid choline
  • Promotes preparation for action
  • Conserves energy
  • Attention
  • Memory
  • Defense and/or aggression
  • Thirst
  • Sexual behavior
  • Mood regulation
  • Ability to play
  • Rapid eye movement sleep
  • Stimulates cholinergic nervous system
  • Controls muscle tone by a balance with dopamine in the basal ganglia
  • Self-consciousness
  • Over-inhibition
  • Anxious depression
  • Depression
  • Lack of inhibition
  • Poor recent memory
  • Alzheimer’s disease
  • Euphoria
  • Parkinson’s disease
  • Antisocial
  • Manic behavior
  • Speech blockage

  • Synthesized from glutamic acid
  • Transmitter glutamate is different from metabolic glutamate
  • Glutamate occurs naturally in protein-containing foods such as cheese, milk, mushrooms, meat, fish, and many vegetables
  • Glutamate is also produced by the human body and is vital for metabolism and brain function
  • One of the most important components of protein
  • Generalized activator of interneural transmission
  • Elevated levels of extracellular glutamate are responsible for neuronal damage and degeneration in brain disorders
  • Rage reactions, including assault
  • Delusions
  • Hallucinations
  • Migraine headaches
  • Hyperirritability
  • Decreased protein synthesis
  • Lack of overall sharpness in mental functions
  • Inability to synthesize GABA
  • Lack of ability to calm oneself
GABA (gamma-aminobutyric acid)

  • Precursor is glutamate, which is synthesized from the amino acid glutamic acid
  • Reduces aroused aggression, anxiety, and excitation
  • Generalized inhibitor of interneural transmission
  • Anticonvulsant
  • Sedation
  • Impaired recent memory
  • Irritability
  • Seizures
  • Huntington’s disease
  • Epilepsy
Endorphins (endogenous opioid peptides)

  • Counteracts the impact of physical and psychologic stress and reestablishes homeostasis
  • Alters the emotional implications of a painful experience
  • Involved in brain reward center
  • Involved in feeding behaviors
  • Involved in growth
  • Involved in memory consolidation
  • Insensitive to pain
  • Movement disorder similar to catatonia
  • Auditory hallucinations
  • Impaired memory
  • Hypersensitivity to pain and stress
  • Inability to experience pleasure

Adapted from Stahl S. Stahl’s Essential Psychopharmacology: Neuroscientific Basis and Practical Applications. 3rd ed. New York: Cambridge University Press; 2008. @

Author: Stephen M. Stahl