Even though I did not use xanax for a month, the last time I did I took large amounts for several days. I am afraid I failed my drug test that I had on day 30 of cessation.

As long as you were prescribed this by your doctor, there is no worry, you may be asked to show proof, and/or need to notify them of the usage.

If this was an illegal usage, yes if this is one of the elements tested for, it will show up

What kind of drug test? It should not show up in urine or blood after a 30 day cessation. If they were to test hair/fingernails, then it most likely will appear.

Sunfire is correct. It depends on the test. Which test was given?

But, Chuck is also correct. If this is a prescription, no worries. Just need to prove that it was prescribed.

Even though I did not use xanax for a month, the last time I did I took large amounts for several days. I am afraid I failed my drug test that I had on day 30 of cessation.
You took "large amounts"? How large?

The half-life of alprazolam has been found to be about 11.2 hours (range: 6.3-26.9 hours) in healthy adults. Even though you had taken large doses prior to your 30 day cessation, it is VERY unlikely that you would test positive for xanax on your drug test.

Can you specify whether this will be a urine test or blood test?

Or is it a hair/fingernail test?

If the drug test is a urine drug test you should be negative. If it is a hair drug test you might have trouble passing a hair drug test.

A common misconception is that if one has a prescription, all is well with you taking it. This is not true. If you are required to refrain from a substance a prescription does not give you a free pass.