Cyclothymia, a bipolar-related disorder that causes milder mood swings between depression and hypomania, commonly co-occurs with substance use and addiction. Diagnosing cyclothymia is difficult, especially when co-occurring with substance use. The milder symptoms of cyclothymia mean that they are often overlooked and assumed to be caused by drugs or alcohol. However, diagnosing and treating both conditions is essential for the best outcomes, for a resolution of symptoms, and for long-term abstinence.