Lexapro (Escitalopram) is an SSRI. Your insurance may want the Dr, to go with a cheaper SSRI or have a justification on why he is prescribing Lexapro. Typical cost control measure.
I'm sorry your insurance is giving you issues. Although I have no idea if it has anything to do with possible interactions. Sometimes it has to do with the dose (this is what happened to me with Lexapro). My doctor wanted to bump me up to 15mg from 10mg per day. Because the pill only comes in 10 or 20 mg my insurance would not cover the 45 pills monthly I would need to give me that 15mg dose per day...frustrating! I moved up to the 20 mg and had no issues with that so it was not too big of a deal...although I would love to be on less if it would have done the same good job with my anxiety issues!
Check with your pharmacist/pharmacist coach on this. Actually, insurance should not deny, in my opinion, unless you are taking a drug that does the same thing or it is not a covered drug under their formulary. (You would check with your insurance to see if Lexapro is on their formulary, because those books they mail out don't always list everything).
Insurance also might, if you are trying to get a tier exception for the name brand medication, recommend the generic or, if there is not a generic, some other drug that is cheaper in the same vein that they feel will do the same thing. You would have to prove why you can't take those other medications for them to grant you a tier exception (depends on the HMO).
It actually should be the pharmacy that would deny you filling it if they see a contraindication, whether it has to do with a drug allergy they are concerned might have implications for you taking Lexapro (ie a related drug), a drug interaction, you are taking other medication that would be vying for the same receptors in your body, or if it would be harmful for you to take with a medical condition you have.
Sometimes my Insurance will deny drugs which have black box warnings or interactions. I have been able to get them over ridden by my Doctor talking to the insurance company.
call your doctor about the stop on this rx by the insurance company and let them work it out. My neurologist did that last month when I was denied provigil - he turned it around in 24 hours. The doctors know what they are doing with the insurance game and know the right things to say to get it approved.