Insomnia due to drug or substance, medical condition, or mental disorder: Symptoms of insomnia often result from one of these causes. Insomnia is associated more often with a psychiatric disorder, such as depression, than with any other medical condition. Surveys suggest approximately 3% of the population has insomnia symptoms that are caused by a medical or psychiatric condition. Among adolescents and young adults, the prevalence of this form of insomnia is slightly lower. 2% of the general population is affected by this type of insomnia. Approximately 3.5% of all sleep-center patients are affected by this condition.