The ''Loveline'' doctor is in. But in lieu of educating teens about Trojans, the sage radio/MTV celeb shares the highs and lows of his 12 years treating drug addicts and alcoholics at Pasadena's Las Encinas Hospital. (MTV connection: It's where Jack Osbourne went for rehab.) The gripping, fast-paced narrative is chockful of curiously intense characters, from a stripper who uses sex to forget about her withdrawal from opiates to a reclusive model with serious mood swings. Written with a healthy dose of humor and poignancy, ''Cracked'' is an addictive read.