Will hydrocodone fail a drug test?

It depends on the test.

A standard 5-panel test, which typically looks for the same drugs on a SAMHSA-5 test consists of:

Marijuana (marijuana, hash)
Cocaine (cocaine, crack)
Amphetamines (amphetamines, methamphetamines)
Opiate (codeine, heroin, morphine)
Phencyclidine (PCP)

Hydrocodone will NOT be detected on a standard test, almost always an immunoassay test. The definition of opiates is not always clear but the most current definition of an opiate refers ONLY to the opiate alkaloids found in the opium poppy, most notably morphine and codeine. Hydrocodone is a semi-synthetic opioid meaning it was made from opiates and is structurally very similar. Some people consider semi-synthetics to be opiates but really they are not. And fully synthetic opioids like methadone and tramadol are not opiates at all. However the term opioid can be applied to opiates, semi-synthetics, and synthetics.

However depending on who is testing they may add on tests including a test to detect hydrocodone.

If you would show up positive for hydrocodone you would be asked if you have a prescription, if you do have a prescription there will not be any problems. If you do NOT have a prescription then it is a problem.