People with depression have a strong suicidal tendency, and many people think that depression is a mental illness. In the middle of the 20th century, medical research found that the concentration of three neurotransmitters (serotonin, norepinephrine and dopamine) in the brain of depressed suicides is lower than that of normal people. Medical scientists speculate that it is the imbalance in the concentration of these three neurotransmitters that leads to depression.
The statement 'The drugs developed to maintain the concentration balance of the above three neurotransmitters are effective in the treatment of depression' gives the above medical scientists the strongest support for their conclusions.