Does anyone have any experience with 5-HTP or L-Theanine or GABA or anything else?
Both the serotonin precursors 5-HTP and L-trytophan are contraindicated if you're taking any serotonergic antidepressant. Their promotion for anxiety and depression is based on a flawed premise, that these disorder are caused by too little serotonin in the brain. The opposite is the case. Antidepressants actually reduce serotonin levels
in areas of the brain associated with anxiety/depression after a few weeks. There is also a risk of developing Eosinophilia–Myalgia Syndrome
Some with very mild anxiety and/or depression claim it helps, but the research shows limited results.
There are two problems with this. Firstly, orally taken GABA can't penetrate the blood-brain-barrier (BBB) so the safest way of taking GABA supplements is to drop them into the toilet and flushing. The results will be exactly the same and you'll avoid the risk of choking on the tablets. There are several GABA analog meds such as pregabalin (Lyrica) and gamma-vinyl GABA (Vigabatrin) which do deliver GABA into the brain, but they have only moderate effects at best, probably because this GABA isn't taken up by GABA receptors and affects glutamate pathways instead.
Secondly, no reasonably well functioning brain lacks GABA. It is a by-product of the process that fuels the brain and is so abundant that the BBB has billions of tiny pumps
to remove the excess.