The brain's chemical balance by increasing the supply of a chemical messenger in the brain. It may take several weeks of treatment before maximum effects are seen. Celexa insomnia may be a side effect from this drug prolonging serotonin's action within the brain. In Celexa insomnia. Although Celexa is noted for its reduced instances of drug interactions, you should always let your doctor know what other medications you are taking. Celexa is an antidepressant drug used to treat depression associated with mood disorders. Depression to worsen and even lead to suicide in a small number of patients. After stopping an MAO inhibitor.