Have you seen a GI about this? It sounds to me like IBSD...

However, note, that Effexor does sometimes cause diarrhea

not sure,,i too have stomach issues, and kidney too so No over counter meds for me, I combat vomiting(frequent)/ indigestion with baking soda and water. Gut is definitely second brain...turkey creates serotonin in gut. good luck. ml

Psych meds that target the serotonin transporter (eg. Zoloft) also effect gut motility. Most of our serotonin is located in the gut and blood platelets (although our brains make their own; there's not a fixed supply), and serves different functions. So yeah, a whole lot of those meds' side-effects come from the effects on peripheral serotonin, including withdrawal symptoms. And like with any med, usually fade over time (but not always, so talk to a gut doc, not a head doc).
(BTW, yeah, the amino acid tryptophan is a precursor to serotonin, but you'll get enough eating just about any vaguely protein-containing food. Thanksgiving dinner makes you sleepy cause of starch, too many calories, some drinks, football, and listening to relatives. Some poisonous plants and bugs straight inject you with serotonin, and in your blood that equals pain and swelling).

No they don't steal Serotonin from you. Most SSRI/NRI meds metabolize similarly, but each drug is different.

In general SSRIs are absorbed fairly slowly with completion taking between 3 to 8 hours. The active drugs in SSRIs bind to proteins and are transported through the bloodstream and metabolized in the liver to varying degrees. The part of the medication that goes to the brain, travels through the bloodstream and crosses the blood/brain barrier to do its job.

The Biopsychiatry and explanation of the Pharmacokinetics of each medication are pretty technical to explain. Researching individual medications and how they work alone or with other medications may give you the answers you seek. I do know that many BiPolars have IBS and take their meds without issue....I had IBS for years and never had trouble with my Psych meds. A lot of these things are very individualized on a per person basis.

Not sure I agree, I tend to agree with the poster above. Unless you are saying to me there is absolutely no way the gut and the brain are joined, which in my opinion is false. If serotonin is bound and taken from the gut to reuptake elsewhere, then surely we are borrowing it from the gut?

And im positive this is what causes the runs etc when first starting effexor etc. Cant prove it. But the biochemistry makes sense, unless there is no way for the drugs to take from our gut to our brain? So then where do they take the serotonin from, or are we saying they dont take any serotonin, they simply reuptake it?