dear patient ,you have asked a very good question. IVig contains a group of antibodies derived from human blood which helps in providing artificial immunity since your blood is deficient in immune cells that produce antibodies which in turn helps in providing immunity. since its a human product,its least likely to interact with your other synthetic medications. Tamoxifen acts only on breast tissue,your anti hypertensive meds are safe ,levothyrox,omeprazole,alendronate,sodium,potassium,gabapentin,donot react with one another or with ivig,none of the meds react with ivig. but here i do want to mention you to decrease the dose of xanax,because there might be slight inteaction of xanax with gabapentin,though not severe but it can increase drowsiness. hope that answers the question.