Antidepressants work by increasing the amount of neurotransmitters available at the synapse. This ultimately results in improved communication between the neurons. Diagnosis Unfortunately, there is no specific blood test to detect a deficiency of seratonin in the brain. Several blood and urine tests have been tested, but have not proven useful thus far. PET scanning is being done at research centers, but is not widely available.
Depression actually causes a decrease in the metabolic activity of the brain.
Depression is seen on the PET scan as a color change from the normal brain. Interestingly, after an individual is treated, the PET scan will revert back to normal. Hopefully, in the future, the PET scanner will become more available, but I doubt if it will ever be used widely for diagnosing depression because it is quite expensive. Therefore, the diagnosis is based on ruling out other conditions that mimic depression and the response to antidepressants. It is important to check for an under active thyroid since hypothyroidism can mimic depression.