How long after expiration can curva be used and what could the possible side effects be if you took them after the expiration date?

Curva: is not a monitored drug by the FDA. Therefore the expiration of this drug cannot be properly determined

Honestly: I wouldn't advise to take either a supplement or a prescribed medication past its expiration date. The expiration date is there for a reason, more often because the drug or supplement does not have the same efficacy past that date. Plus, in supplements that aren't regulated by the FDA you really don't know what you're getting when it starts to degrade past it's date. I'd say throw them out.