"As with any drug, there are withdrawal symptoms the addict experiences upon cessation of cough syrup use. Cough syrup, or DXM, affects the body in many ways. Becoming addicted to the medication results in a loss of control by the individual addicted to the medication. Things that once used to interest the addict become erroneous. Interest in sports, academics, and extracurricular activities fades. The addict often finds himself or herself obsessed with seeking out cough syrup, ingesting cough syrup, and scoring drugs to counter the withdrawal effects of cough syrup. In order to combat withdrawal symptoms, many cough syrup abusers report using Benzodiazepines such as Xanax which enhance the effect of the neurotransmitter gamma-aminobutyric acid, which results in sedative, hypnotic-like results. In addition, the addict may turn to alcohol, marijuana, and other drugs to avoid feeling the unpleasant withdrawal symptoms, which include depression and mood swings. Withdrawal from cough syrup can be a very disheartening experience. According to the National Highway Traffic Safety Administration, long-term use and subsequent withdrawal of DXM involves symptoms such as insomnia, dysphoria and depression. DXM addicts also complain of itchy skin. The hardest part of DXM detox is the depression. The dissociative effects cause psychological issues with some recovering drug abusers such as psychotic episodes and night terrors. "
http://www.thehillscenter.com/addiction/cough-syrup/
Here's an old thread on the same issue that may be helpful.
http://www.medhelp.org/posts/Addiction-Substance-Abuse/Need-help-quiting-cough-syrup/show/446693