This is the 2007 version. Click here for the 2017 chapter 02 table of contents.


Serotonin (sara-TOE-nin)-technically known as 5-hydroxytryptamine or 5-HT-was one of the first neurotransmitters discovered. During the 1960s, researchers noticed that serotonin resembled LSD in chemical structure. Reducing serotonin levels in rats with special toxins (selective poisons) produced symptoms associated with "bad trips." Rats become hyperactive, frightened by novel environments, and generally anxious in appearance and behavior (Ellison, 1977). Not all serotonin-reducing drugs have this effect, however. Several types of serotonin receptors exist. Some compounds block serotonin more profoundly than LSD without producing psychoactive effects.

What are indications that serotonin can alter mood or emotion?

How does Prozac effect serotonin?

What does St. John's Wort do?

Serotonin may also be involved in other changes of mood and consciousness. For example, serotinergic receptors are prominent in the raphe nuclei of the brain stem, which regulate sleep and dreaming.

Prozac, the anti-depressant medication that became extremely popular in the mid-1990s, works by raising serotonin levels. An herb called St. John's Wort works the same way. Its effects are milder and slower to occur than prescription antidepressants. Nevertheless, St. John's Wort is the single most-used herbal remedy in Germany.

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