Vorinostat - HDAC Inhibition - Fear Extinction, Learning, Memory enhancement
Warning: These compounds have only been used for cancer so far, so other use cases are in their infancies. They are very powerful and can stop cell cycles which is how they kill cancer. They cannot be taken daily and research points to far lower doses than cancer treatment
Vorinostat is a pan-HDAC inhibitor of sorts, inhibiting HDACs 1, 2, 3, 8, 9 and more to one degree or another (mostly Class I, some Class II).
Neurostat (unknown structure, few studies) and Crebinostat (known structure, few studies) are HDAC inhibitors meant directly for memory and fear extinction, but are more expensive and harder to find than vorinostat. There are many other HDAC inhibitors, mostly used for specific types of cancer, but they are either much more expensive or not as useful
Butyrate is also an HDAC inhibitor and it is a waste product of your gut bacteria. This can be boosted, but is difficult because of the diet requirements to do so.
HDAC inhibitors are currently being research for fear extinction, and other novel uses this is because HDAC has a very novel mechanism of action which allows genes to be turned on when they should be turned off.