Mrs. Dubose's addiction to morphine, as depicted in Harper Lee's To Kill a Mockingbird, can be defined as a representation of the heritage and culture of the South during the time period of the novel. While Mrs. Dubose wishes to sever her dependence upon morphine, the cultural significance of her addiction is far more prevalent.
Figuratively, the drug induced stupor Mrs. Dubose lives in illustrates the South's refusal to change its prejudicial thoughts. Instead of fixing the problem (figuratively removing the morphine), the South refuses to identify an issue exists. This said, Mrs. Dubose does recognize the problems. That said, she could have simply laid back and died with the morphine running through her veins (the prejudice). Instead, she recognizes the problem and commits to eradicating the morphine from her system.
Essentially, Mrs. Dubose's addiction illustrates the depressive state of the South. How they would, figuratively, rather stay like they are than see change. The hold racism has on the South possesses the same power the morphine has on Mrs. Dubose.
Since Mrs. Dubose requested that Jem read to her every day as punishment for his vandalism of her garden, was it not her intent to persuade the youngster that Atticus's attitude toward blacks was wrong and not in keeping with Southern traditional culture. Her phillipic outbursts were meant to show him and, of course, Scout the error of their ways in believing Atticus was correct in his belief. Mrs. Dubose's realization of her addiction and her subsequent battle to end it was right on point. She did not want to "go quietly into that good night." Rather she wanted to reform herself and the youngsters to exemplify traditional Southern values. As such she is a relic of the past and this is why Jem reacts violently toward her originally. It also explains why Atticus must present her as a very sick old lady who fought the good fight to recover from her addiction. Jem is understandably confused, yet he perceives that there was evil in what Mrs. Dubose tried to uphold as right.