What causes the "Absinthe Effect"?
This is a very good question. The source of the "Absinthe Effect" has been considered since the introduction of this magic elixir in the 1700's. There is actually still a debate over whether or not the absinthe effect truly exists. I can tell you that I have experienced the absinthe effect and continue to do so on a regular basis. My wife believes too regular a basis but that is another story.....
It is known that more than one herb used in the production of absinthe exhibits psychotropic properties. Psychotropic substances effect the CNS (central nervous system) to alter brain function. Such alterations can manifest as changes in mood, perception, consciousness and behavior. Having a background in pharmacology, bio-chemistry and chemistry has allowed me to research this topic to some extent and put it into easy to understand language for you.
As mentioned, there is more than one substance acting on the CNS in Absinthe. We will concentrate on the substance known to have the most prominent effect. In addition to alcohol, absinthe's major constituent is Thujone. Thujone is the chemical compound derived from the herb Artemisia Absinthium or Wormwood (aka Grand Wormwood). There is complexity involved in classifying the different Species and Genus of this plant class (such as the amount of thujone contained in the different species) that go beyond the scope of this article. For our purposes, we will refer to it simply as Wormwood or Thujone.
Thujone was once thought to act on the area of the brain that responds to THC (marijuana) as their chemical structures are somewhat similar. This has been proven false. Thujone is now known to act on a receptor in the brain known as the GABA (gamma-aminobutyric acid) receptor. When activated, the GABA receptor basically tells your brain to slow down and relax. Thujone is a GABA receptor antagonost (inhibitor). Basically, thujone prevents the GABA receptor from telling your brain to relax and slow down. This causes stimulation and alertness.
It may be helpful to understand that some drugs have the opposite action of Thujone. These drugs are GABA receptor agonists (as opposed to antagonists). They increase the GABA receptors message to the brain to relax. These medications are used for various purpose such as relief of anxiety. Drugs in this class include Benzodiazepines like Valium or Xanax and Barbiturates like Phenobarbital. So what Thujone does is basically the opposite of taking Valium. It tells the brain to wake up!
While speaking about GABA activity, it is also important to note that the alcohol in absinthe acts on the GABA receptor as an agonist much like a Valium. So while under the influence of Absinthe, you would be experiencing a push-pull effect from the Thujone vs the alcohol. The full relationship of how these 2 substances react with each other and their combined effect on the human brain is yet unknown. Although their CNS activity is not completely clear, it would be prudent to say their combined effect may be responsible for some, if not all, of the "Absinthe Effect"