Welcome to JustAnswer!
Thanks for your question.
It seems like you are not multiple medications. In that case, interaction between medications is an important issues. The likelihood of interaction is also more as you are taking several medications. Based on your description, it seems like you are already on several medications, and now you want to consider Xenical. I just wanted to let you know that Xenical may decrease the levels of thyroid
medication by inhibition of gastric absorption. In order to resolve this issue, Xenical should be taken at least 4 hours apart from thyroid medication.
As far as interaction between your ongoing medications is concerned, I am sure you are aware of all those minor issues such as diclofenac may decrease the effect of lisinopril, omeprazole may increase the level of or effect of amitriptyline and diclofenac. If you are following your doctor's advice and getting regular follow-up, then you might have adjusted to your existing medication.
It is just that adding Xenical will require 4 hours gap. You can discuss all these things with your doctor and plan things accordingly. It is also important to cut down/ reduce the amount of medication/pain medication as long as you can. You can visit a pain management doctor for managing your medications.
Please let me know if you have any other question for me.