The jet antidote is unique in that it can be used an infinite number of times without being consumed, effectively allowing them to use jet anytime they want without fear of addiction. Players who use the unofficial patch, however, cannot do this: they have to buy more in San Francisco.
The antidote can be used on Myron. In this case, however, it will be consumed.
If one doesn't find the right track to find the cure they can get it from the gun merchant on the PMV Valdez, who (curiously) carries almost no guns but loads of drugs, plus has several vials of jet antidote which are replenished if one buys them.
Discovering the cure throws a wrench in Mordino's plan to take over Redding. It also ensures that Redding joins forces with Vault City in the ending.