For over 30 years, methadone has been used to treat opioid addiction. Since methadone is effective in reducing withdrawal symptoms, it is used as a method of detoxification for opiate addicts. However, methadone is not effective in treating other drugs of abuse, such as cocaine. Tiagabine is a drug that enhances levels of gamma aminobutyric acid (GABA), a chemical found in the brain and spinal cord. The objective of this study is to determine the effectiveness of tiagabine in modifying cocaine-using behavior and reducing opiate withdrawal symptoms among newly admitted methadone-treated patients.