When the police (or courts) release you on the condition that you adhere to a set of strict rules e.g Don't leave the country, don't do whatever you did in the 1st place again etc, and also that you appear to answer your bail at a location selected by the police/courts i.e your nearest police station
Failure to do so, or "to breach your bail" would result in a warrant been issued for your arrest
Scott - "Shit, I gotta go man. My bail coditions say I'm not allowed to be any where near you an the police are over there"
Dan - "You best get the fuck out of here then mate"
Something a doctor would prescribe to a Heroinaddict, usually by way of bail conditions issued by the courts, which BLOCKS the effect of any Heroin taken or gives the user undesired effects e.g Nausea, shakes, cold sweats etc
Commonly used in the Castleford, England area among others
"Maffys on the blockers again, he got caught shop lifting an the courts included taking them as part of his bail conditons. There going to test his piss to make sure he's taking them" said Liam to Dan