There’s a bit more research in China: Regulation of GABAA and 5-HT Receptors Involved in Anxiolytic Mechanisms of Jujube Seed: A System Biology Study Assisted by UPLC-Q-TOF/MS and RT-qPCR Method - PMC
Alkaloids in jujube (in this case the study was done on jujube seeds, but these alkaloids seem present in the fruit as well) cause up-regulation of GABA and serotonin receptor production. It’s possible that’s the reason for the effects and for that 2004 acute reaction to venlafaxine.
There are other food components found to do the same, though: omega-3, some polyphenols and flavanoids (present in many fruits and vegetables), and curcumin (in turmeric).
As far as I know, no one recommends avoiding these other foods when on anti-depressants. Not to mention there are plenty of behaviors that can up-regulate serotonin receptor expression, like physical exercise. So there must be some kind of threshold for how big the effect needs to be, before it can precipitate SSRI/SNRI-induced serotonin syndrome. And I’m sure that threshold is different for different people. It’s well known that some people tolerate larger doses of the same medication than others – is this because, in addition to genetics, some people get more exercise or eat more fruits and vegetables (or get more sunlight, or have lower stress levels, or get better sleep, etc.) and thus have greater or lesser sensitivity to serotonin (due to higher/lower behavior-induced receptor density)?
I’m watching a lecture series on human behavior, and several lectures are focused on the complex interplay of genetics and environment, and I’m struck by how unbelievably dense the web of interactions is. You could research jujubes (or any food) for 100 years and find millions of effects it has on mRNA expression and the regulation of various pathways, but amazingly (at least to me) you still wouldn’t know if it’s okay to take with SSRIs until you did a clinical trial and saw that 5 extra people out of 100 had an adverse reaction. And even then you still wouldn’t know if you’d be one of the 5 people or one of the 100 until you spent another few decades researching the genetics and behavioral differences between those two groups and which group you’d likely fall into. Incredible!
Back to your original question though: I suppose it’s better safe than sorry, and people taking serotonin-increasing drugs shouldn’t take any of the obvious culprits that seem to have marked subjective effects. Maybe 1 in 5 times I eat jujube I really note a subjective, psychological effect. I don’t note this when I eat blueberries or take a fish supplement or lift weights (well, maybe 1 in 10 times from lifting weights, though I know others who feel great after ever workout – lucky bastards). So perhaps jujube is slightly stronger in its effects and is worth avoiding. On the other hand, when one eventually weens off their serotonin-increasing drugs, it’s equally worth trying to increase jujube consumption (as well as polyphenol/flavanoid rich fruit and vegetable consumption, physical exercise, early morning light exposure, improve sleep hygiene, etc. – all the myriad behaviors known to modulate serotonin receptor density/sensitivity) to see if that helps with symptoms post-medication.