Here is an account of long term centrophenoxine use. Not sure there is lots of study demonstrating 35 years of use is safe in large qty of the population so this should be treated as an anecdotal report only. It does cite other study he has done.

http://www.longecity.org/forum/topic/64596-my-personal-35-ye...

There are links to outcomes of studies on oxiracetam here which is my go to racetam:

https://examine.com/supplements/oxiracetam/