Since 1997 Bulgaria has operated under a currency board arrangement (CBA), which is an exchange rate regime where a country commits to keep its local currency to a fixed exchange rate against an anchor currency. For Bulgaria, that anchor currency is the Euro.

Given this, any discourse about how Bulgaria's entry into the Eurozone implies a dramatic change to its monetary sovereignty is likely unfounded. It didn't happen overnight - it's been an almost 30 year long process. Joining the Eurozone does, however, remove the pegging frictions for Bulgaria, and allows them to fully integrate into the monetary union.