Hi, Shirl -

Effexor and Pristiq are virtually the same. Pristiq is a chemical that is generated by Effexor once it's metabolizing in your body. They don't have exactly the same levels of effectiveness for some reason (effexor seems to show better results) but operate in the same way on the same neurotransmitters. When prescribing combinations of medications, doctors want to add something that works on a different neurotransmitter - or in a completely different way - so that the two drugs complement each other. Instead of effexor and pristiq together, it would make more sense just to increase the dose of one if more of the same effect were desired.

I'm not sure what you mean by a "sensitive system". Each medication has many possible adverse effects, but it's not the same for everyone. People react differently depending on the ways their bodies handle various chemicals. A recommendation of this sort should come from a doctor who is thoroughly familiar with your medical history and previous experience with medication.

John