Slappers were steroidal patches of synthesized Venom. Jackson Chappell, the nurse of an elderly and withered Bane, created them after he had managed to obtain the venom formula from Bane. Bane's addiction to venom had broken his body, and he needed venom to muster the energy to stay alive.
Slappers were popular with high school athletes. Its addictive nature was detrimental to the body, as the dose seemed to last shorter every time.