I don't believe Enbrel is really used for crohns. I'm not certain of the reason, but it definitely makes no sense for them to put you on Enbrel over humira given they probably cost about the same. In fact I would forward this
http://content.nejm.org/cgi/content/extract/350/8/840 to your insurance company and tell them you are requesting a review of the approval. Contact your state insurance commissioner as well and find out if there is an independent medical review process for the medication. Basically your insurance company forced you to a medication which has no apparent benefit to IBD and you have a right to be put back on the proper medication. Make sure you talk to your state insurance commissioner here in Cali because there is a process that an outside reviewer can do for you that binds the company if you don't agree with the decision of your appeal process. Make sure to appeal this immediately and inform the company they have 30 days to make a decision but you expect one sooner given the severity of their decision that was clearly not made based on the standard of care for your disease.
Also have you been on remicade? This is important because that would be the drug they switch you to as a standard of care as a first line anyway unless you had already been on it and failed. DO NOT take the enbrel and contact your GI immediately and get them to help you with the process as they might have to talk to your insurance company anyway. Good luck and hopefully you can get this fixed right away.
Also what insurance do you have as I have experience with blue cross, aetna, pacific care/united health here and they all do in fact cover the medication whether they like it or not. Also some doctors offices will inject you and bill it as a procedure...if it's a ppo your insurance really can't tell you otherwise (also if its a ppo they have to go with a treatment your doctor prescribes if the drug is approved for the treatment and on their list of drugs. They have no right to force you to a medication on a ppo, as long as it is covered and you have other covered options). If it is an hmo you are a little less in control, but even then they have a duty to give you a proper standard of care and in this case, it clearly is a medical failure on their part and you can make a big stir about it, it will just take time.