Aniracetam is definitely a potent and clean anxiolytic IME, but very short lasting, like 2-3 hours, also really fucks with my sleep unfortunately. That said, when I did take it for anxiety I'd never taken a benzo, z-drug, gabapentinoid, or any other substance that is POWERFULLY anxiolytic, so not sure if my opinion would be different if I'd already primed my brain to expect proper anxiolysis rather than the "subtle" effect of most of the more benign nootropics, racetams and similar.
Tianeptine I do find to be anxiolytic also but it does seem to be true that lower doses have a more sustainable long term benefit, ie, when I was taking sub 25mg doses a few times daily after a while I did notice I was overall more level headed, less anxious, my mood was more stable, etc. If you dose to the point that the opioid effects are really prominent, then I think tolerance and receptor downregulation and all that annoying neuroadaptive stuff destroys the longer term benefits that can come from low, steady doses. That said - I think it has been shown that the mu agonism plays a key part in the antidepressant effects, IIRC mice with a deliberate genetic alteration to delete this receptor did not get any of the positive effects (before they were sadly euthanized and their brains dissected, no doubt). It is also a serotonin reuptake enhancer of course, one of the only such substances known, again IIRC, so this no doubt plays some role in it's benefits but again probably is only relevant at lower doses, possibly with a regular schedule - unlike with single large doses when it starts to act essentially like any other opioid.
