All the processes, both intellectual and emotional, depend on the special chemical reactions performed in the brain by neurotransmitters - special molecules that transmit information trough the space between neurons. These reactions are possible due to the fact that neurotransmitters are able to exchange the signals with each other. Decreased or increased signaling make us respond to the reactions by changing the mood, behavior, feelings, and/or emotions. The signals are transmitted in the form of electrical stimulation.
The health of the brain depends much on the balance of the different neurotransmitters. When the balance is disturbed, it may cause various disorders of intellectual activity and emotions. To increase signaling in the brain is possible by healthy food and products, with the help of the healthy mode of life, physical exercises, and so on.
Tiredness of the brain, or state of emotional exhaustion, is familiar to those people who are used to working hard mentally without having a rest. Often, this feeling of tiredness may arise with preparing for difficult exams, or fulfilling urgent and very important work. The brain cannot increase signaling, also because of the stress that may lead to emotional tension and depressions. Sometimes the chronic state of lethargy is connected with congenital deficiency of certain neurotransmitters in the brain.
Narcotics, such as stimulant amphetamine, drugs of the opioid group, alcohol, nicotine in tobacco, and many other psychoactive substances, influence a lot the activity of the neurotransmitters, especially those that are responsible for positive emotions, pleasure, joy, etc. They substitute the effects of neurotransmitter processes and increase signaling between them. With using narcotics frequently, neurotransmitter dopamine is produced permanently, and gradually the stocks of it run down. It causes nervous exhaustion, psychological disorder, and/or a breakdown.
New doses of the drug increase signaling and restore the lost neurotransmitters in the brain. The user feels better. The organism tries to fight for living, and proceeds with producing more neurotransmitters. They are accumulated in the body in great quantity and, after this, the organism begins to destroy them. Without the narcotics, all the natural processes are disturbed, and the brain fails to produce enough chemical substances that are required for positive state, emotions, and mood. In order to restore them, an addict takes another dose, and his organism goes on being destroyed. Thus, the physical addiction develops.