Interesting interaction question - how much tramadol and tianeptine are we talking about here?
I don't know about synergistic, but there is potential for a bad reaction if you take both drugs (although it is really uncertain how high the risk is and if it even exists...)
Firstly tramadol is known for having the potential to cause seizures, especially at high doses.. although there has been a report on here of someone having a seizure after just 300mg. 400mg is the generally accepted safe max in 24 hours, but people clearly vary greatly in their seizure potential. The risk is increased hugely if it is taken with
other drugs which might lower the seizure threshold (lowering the threshold makes seizures more likely.)
Tianeptine is a tricyclic antidepression, and tricyclics can indeed lower the seizure threshold - however after doing some reading it seems that the risk is a lot lower with tianeptine than for other tricyclic antideprssants, and it is suggested as a good choice of antidepressant in epileptics! There is quite a lot of conflicting information out there - I would say there is
potential for a bad interaction, but then again
this research found that tianeptine actually delayed the onset of seizures in mice and may be protective against seizures. Given all of this uncertainty, it's impossible to say what the risk is - but I am a very cautious person, and don't really combine tramadol with anything at all, just in case, let alone a tricyclic antideprssant.
Secondly, tramadol is a funny drug and has some serotinergic action as well as opioid action, and tianeptine may also have some serotinergic activity, although as with it's effect on seizure threshold this isn't certain (and it may actually decrease serotonin levels as opposed to other antidepressants..)
If it
is serotinergic (causes release of serotonin), then taking two serotinergic drugs together has the risk of causing "
Serotonin Syndrome" which is rare but can be fatal - I have known a few people who got this comining tramadol with other serotonin releasing drugs, but no idea how big the risk is here (or even if there is one.. )
Essentially, tramadol is a tricky drug to safely combine with a lot of things, and tianeptine is an unusual antidepressant compared to the other tricyclics and SSRIs and is not very commonly known about - so although it may well be perfectly safe, I suspect it will be difficult for anyone to tell you definitely.
I used to take amitriptyline, another tricyclic antidepressant, and didn't notice any synergy with opiates, incidentally.. no experience with tianeptine however.