The neurotransmitter Serotonin is primarily in the gastrointestinal tract, but it plays an extremely important role in human brain function. Studies have linked the activity of Serotonin in the brain with the expression of anger/aggression, mood, sleep, appetite, and even sexual drive.
(Drugs such as psilocybin, DMT, mescaline, and LSD can mimic the effects of this neurotransmitter in the brain, and Ecstasy can force it's release, but today we're looking at just prescription medication. We'll get to those others later.)
In cases of clinical depression, the amount of Serotonin available in the brains of affected individuals is lower than that of the general population. This is especially true of people who suffer from eating disorders or loose their ability to eat due to depression. Lower caloric intake necessarily results in decreased energy production; resulting in the creation of a negative feedback loop. The less you produce, the worse you feel.
So, to deal with this problem, people suffering from the symptoms of depression are often prescribed Selective Serotonin Re-uptake Inhibitors.
Today the role of Serotonin will be played by Welsh Corgis.
Normally, the brain is able to produce sufficient amounts of serotonin to maintain normal brain function, and the owners of said brains are able to maintain a relatively stable outlook on life. This is because, when serotonin is released into the synapse, enough binds to the post-synaptic cell to trigger the cell to fire.
Here's a neutral view of the synapse:
Now in a normal brain, it doesn't matter if all the serotonin molecules end up binding to the post-synaptic receptors. As long as there is enough to continue the neural chain reaction, it doesn't matter if the remaining Serotonin is reabsorbed back into the pre-synaptic cell.
In depressed brains, where there isn't very much Serotonin available, or ones that are simply unable to release enough in time to continue the reaction, this is a problem. Unless all the receptors necessary are activated, the impulse fails.
We need AT LEAST three corgis here, or the signal will not continue.
This is where SSRIs come in. Like putting a slide out front, the Serotonin can get out, but they can't get back in. They have nowhere else to go but the post-synaptic cell because their tiny little Corgi legs make them too short to get back up.
Ha ha haaa... I made myself sad.
Unable to return to the neuron from whence they came, serotonin is forced to bind with the post-synaptic cell. This forces the brain to operate in almost exactly the same way as it would under healthier conditions.
That's the idea anyway.
There are several important facts worth mentioning before we wrap this up, however.
Efficacy: While SSRIs are effective at treating severe depression, a 2010 meta-analysis of existing data failed to find any significance difference between mild-to-moderately depressed patients treated with SSRIs and those given placebos.
Sexual Side Effects: SSRIs have been shown to cause numerous sexual side effects in 17-41% of patients; these include a diminished libido, erectile dysfunction, and the inability to achieve orgasm. This is due to the fact that continual stimulation of the post-synaptic cells can diminish one's ability to react properly to the release of dopamine.
Suicide Risk and Aggression: While there have been observed links between SSRI use in adolescents and an increased likelihood of suicide attempts and aggressive behavior, no such link has been as clearly established regarding adult users.
Discontinuation Syndrome: Like all other antidepressants, SSRIs can cause dependency in users. In some cases, the effects of discontinuation can be almost identical to the depression that caused the patient to seek treatment in the first place. It is important to discuss the risks and the weaning process with your doctor before beginning any SSRI regimen.