A Quincy attorney pleaded guilty Tuesday to charges he tried to sneak prescription drugs used to treat drug addiction to someone at Chelsea District Court in November, authorities said. Michael Lustig, 45, was charged with possession with intent to distribute drugs. He was sentenced to 18 months of probation, during which he must undergo treatment for substance abuse, submit to random drug and alcohol testing, and receive counseling, the Suffolk district attorney’s office said. Lustig used his attorney credentials to bypass security, the office said.Catalina Gaitan can be reached at firstname.lastname@example.org. Follow her on Twitter at @catalina_gaitan.