When De Quincey began using opium in the autumn of 1804, he described this substance as capable of opening his mind and bringing order and harmony to his thoughts and feelings. However, shortly after, he began to suffer from visions, hallucinationsHallucination/hallucinating/hallucinate, and nightmares. If the intoxication of opium guaranteed the writer greater artistic freedom and fluency in writing, at the same time, it undermined his social life and physicalPhysical and mentalMind/mental health. Other authors of the long nineteenth century, such as Samuel Taylor Coleridge (1772–1834) and John Keats (1785–1821), had similar experiences, and testimonies of the impact opium had upon their lives can indeed be found in some of their most suggestive poems. Comparing the side effects of opium abuse described by Romantic authors with recent medical research on the relationship between the use of opiates and sleep disorders, this chapter explores what new light the findings of contemporary medical researchers can retrospectively shed on the writings of Romantic opium eaters. In order to do so, special attention is paid to studies highlighting the creative power of drug consumption, the negative side effects it produces, and how it affects the subject’s general perception of surrounding reality as well as sleep.