I've reread this section of the BBB several times and am still confused. Do you have to roll every combat pass or just once? What happens if you fail on one roll? Help. Help. Help.

Thanos

Depends on the drug. Narcoject is a single test at the end of the round and no furthur side effects. Some have an initial damage, an effect with duration, and then a "downer" damage at the end (those may only be in M&M, not sure). If only one damage code is listed, it's probably the initial dosage damage. If more details are given, follow those.