Collecting this in one place because it comes up every few weeks and the answer is always assembled from scratch. It is about cost and coverage, and it is deliberately narrow — everything I am not confident about is marked as such.
What is actually established
Denials are usually procedural rather than clinical, and the order that works reflects that. Get the denial reason in writing, because it names the criterion you failed. Then supply the documentation that criterion asks for — usually documented BMI with a comorbidity, or a failed prior therapy. Then appeal, and ask for a peer-to-peer review, because a prescriber talking to a reviewing clinician resolves a large fraction of denials that written appeals do not. Manufacturer copay assistance is separate and applies mainly to commercial insurance, and patient assistance programmes are means-tested rather than a discount.
The condition it depends on
Coverage criteria are plan-specific rather than insurer-specific. Two people with the same insurer and different employers have different rules, which is why "my insurer covers it" is not transferable information.
What I am not sure about
What I am after is what actually works on a prior-authorisation denial, as opposed to the list of things that sound like they should work. If the honest answer is that nobody knows, that is a useful answer and I would rather have it.
— InsuranceTom · corrections welcome and will be edited into this post with credit