BTW I only just realized that although tianeptine doesn't have particularly high MOR affinity, it's efficacy is higher than that of DAMGO so technically it's a superagonist. Generally speaking this is considered to make it less desirable as an analgesic because it will produce more side-effects than an agonist. Acute negatives are respiratory depression and sedation, chronic negatives are a rapid development of tolerance and dependence.
That appears to fit it with people's experience of tianeptine. Not that potent BUT producing a really unpleasant withdrawal syndrome.
I only know of the horror stories from Russia where people were injecting the drug to avoid withdrawal syndrome... but given remarks on this thread of it turning into a kind of glue, it won't be any surprise to learn that people were losing limbs because it has a tendency to cause blood clots.
Tianeptine costs $4400/Kg when bought through a legitimate supplier but it doesn't look like much of it is officially bought or sold, possibly because it's use as an antidepressant it still under an active patent although the actual drug was patented in 1970. US 3758528