The central and peripheral nervous system, the hormonal glands (endocrine system), the immune system and the psyche form a network in which the individual components depend on constant information exchange and continually influence one another. Neurotransmitters, like hormones, are messenger substances in this complex network which – by means of precise coordination between the excitory and inhibitory neurotransmitters – allow the system to adapt to the respective situation.

However, constant emotional or physical stress may, if regeneration and recovery are not sufficient, result in a neurotransmitter imbalance and symptoms such as exhaustion, malaise, sleep disturbances, chronic fatigue etc.