You can develop dependency for diet soda due to the caffeine it contains. Caffeine and alcohol are chemically addictive. Many caffeine consumers may be unaware of their physical dependence because their frequent habitual consumption precludes a period of sustained abstinence (e.g. 2 days), according to John Hopkins Medicine. Also, low doses of caffeine can partially suppress withdrawal symptoms. Symptoms of withdrawal from both include irritability, headaches, fatigue, anxiety, vomiting, and stiffness.