EDWARDSVILLE Many young heroin users start with raiding the family medicine cabinet for painkillers and move to street dealers when the supply runs out, the Madison County prosecutor noted Wednesday in making a plea for awareness. Parents can help interrupt the cycle by disposing of unused opiate medications and locking up the rest in a simple $10 or $20 home safe, State's Attorney Thomas Gibbons said at a news conference here. He said heroin is often less expensive and more readily available than prescription drugs. Gibbons and Coroner Steve Nonn said the county will take part in the national "Lock Your Meds" campaign, sponsored by the National Family Partnership. The Drug Enforcement Administration estimates that 70 percent of the nation's 7 million prescription drug abusers get their supply from relatives or friends. The campaign urges secure storage and close monitoring of prescription pain relievers, tranquilizers, sedatives and stimulants and over-the-counter cold, cough and sinus medications that contain dextromethorphan.