How long will nicorette (nicotine gum) gum be effective after the expiration?

It Depends . . .: The degradation of medicines is mediated by atmospheric pressure, temperature, humidity and the ph of the surrounding environment that you kept the gum in. No one can tell you without testing it in a lab, how much nicotine is still active in the expired gum. Rule of thumb is this, the longer its been expired the less likely it is to have nicotine in it that hasn't degraded and become useless.