Depression is a mental disorder manifested by depressed mood, sadness, pessimism, low self-esteem, antisocial behavior, insomnia, fitness weakness, the lack of willingness and strength to live, the presence of anxiety. One of the major causes of depression is a reduction of the level of neurotransmitters in the central nervous system (serotonin, norepinephrine, and dopamine).
Pharmacological antidepressants (eg. SSRI, Prozac) show high therapeutic efficacy, however, they are not free from side effects and, in some cases, side effects can overweigh the positive effects of the treatment. An alternative to psychotropic drugs are natural substances (eg. SAM-e), herbal extracts (eg. St. John's wort) and neurotransmitter precursors (eg. 5-HTP), having similar therapeutic properties without causing side effects at the same time.