Martine Mussies
Maastricht, Netherlands

Since the earliest long-term sea voyages, from the Age of Exploration to the eighteenth century, sailors have been known to report seeing mermaids—enigmatic creatures with human-like upper bodies and fish-like tails. These accounts have long been a subject of fascination and speculation. Could these sightings have been influenced by the use of psychoactive substances?

Historical context of mermaid sightings

The notion of mermaids existed in folklore long before European sailors began to report sightings of them. Notable figures, including Christopher Columbus (1493), Henry Hudson (1608), and Benjamin Franklin (1736, 1769), documented encounters with mermaid-like creatures. Columbus, for instance, reported three mermaids off the coast of the Dominican Republic, noting that they were “not as beautiful as they are painted.”¹ Henry Hudson’s crew described a mermaid with “a woman’s torso and the tail of a dolphin,” while Franklin mentioned sightings off Bermuda and Brest, which gained traction in contemporary publications.²

These sightings reflect the period’s fascination with the unknown, shaped by limited zoological knowledge and the popularity of wonders in scientific discourse. The concept of mermaids played into Enlightenment-era debates on the origins of humanity, with some naturalists speculating on aquatic human ancestors.³ Today, historians largely agree that many of these reports likely described marine mammals such as manatees and dugongs, whose features could be mistaken for humanoid figures, particularly under the influence of psychoactive substances.⁴

Psychoactive substances on ships

Alcohol was an essential part of daily life aboard European ships. The British Royal Navy issued daily rations of beer, wine, or rum to sailors, both as a source of sustenance and a means to prevent waterborne illnesses.⁵ Strong spirits such as rum and gin were often consumed in excess, particularly during periods of stress or monotony. Chronic alcohol consumption has well-documented effects on cognition and perception, with high doses leading to hallucinations and sensory distortions.⁶

Opium, used medicinally for pain relief and sedation, was widely available on ships through European trade networks, particularly via the Dutch East India Company (VOC).⁷ Opium’s effects on neurotransmitters such as dopamine and serotonin induce dream-like states, which, combined with sensory deprivation at sea, could have led to hallucinatory experiences. Some sailors may have consumed opium recreationally, seeking respite from the harsh conditions of maritime life.⁸

Tobacco, introduced to Europe in the sixteenth century, was commonly smoked or chewed by sailors. Nicotine stimulates dopamine release and, in high doses, can cause hallucinations and cognitive distortions.⁹ The interaction of nicotine with alcohol and opium may have intensified psychoactive effects, further altering perception. Combined with the monotonous sensory input at sea—where sailors stared at the vast ocean for months—these substances could have heightened suggestibility and perceptional distortions. The neurological effects of prolonged substance use, including delirium tremens (caused by alcohol withdrawal), further contribute to this theory.¹⁰

The “Set and Setting” of sailors

The experiences of sailors at sea were profoundly shaped by both their psychological state and the environmental conditions in which they lived. Norman Zinberg’s Drug, Set, and Setting model provides a useful framework for understanding how these factors influenced drug-induced hallucinations. According to Zinberg, the effects of a substance are not solely determined by its pharmacological properties but are also shaped by the user’s mental state—the “set”—and the broader circumstances in which the drug is consumed—the “setting.”¹¹

The psychological strain on sailors was immense. They endured prolonged periods of isolation, harsh discipline, and the ever-present threat of death. Their journeys often lasted months, or even years, with little opportunity for respite. The combination of chronic stress, exhaustion, and sleep deprivation left them highly vulnerable to hallucinations and perceptual distortions.¹² Moreover, sailors’ existing beliefs and superstitions played a significant role in shaping how they interpreted their experiences. Tales of sea monsters and mermaids were widespread in maritime folklore, and many sailors embarked on voyages already convinced of their existence. This predisposition likely heightened their suggestibility, making them more prone to interpreting ambiguous visual stimuli as evidence of these mythical beings.¹³

Beyond individual psychology, the physical and social environment of life at sea further contributed to these hallucinations. The vast, featureless expanse of the ocean, combined with long stretches of sensory monotony, created conditions ripe for perceptual distortions. Extended night watches and the dim, flickering light of lanterns could make it difficult to distinguish reality from illusion, particularly when compounded by intoxication. In this setting, a half-seen shadow on the waves or the fleeting glimpse of a marine creature could easily be misinterpreted as a mermaid. Furthermore, the social dynamics of maritime life reinforced these interpretations. Storytelling was an essential part of shipboard culture, and exaggerated or misremembered sightings were shared and embellished among crew members. Over time, these narratives became embedded in collective memory, further solidifying the belief in mermaids.¹⁴ By considering the interplay between sailors’ mental states and their extreme environment, it becomes clear how the combination of psychoactive substances, stress, and folklore could have given rise to their vivid accounts of mermaid sightings.¹⁵

Misinterpretations and memory

Pareidolia—the tendency to perceive meaningful patterns in vague stimuli—may explain why sailors saw human features in marine animals. Combined with the mind-altering effects of the lack of nutrition,¹⁶ the abundance of alcohol,¹⁷ and the use of psychoactive plants,¹⁸ this psychological tendency could have led to mistaken identifications. Historical and zoological studies suggest that many mermaid sightings were actually manatees and dugongs. These creatures have five-fingered bones in their flippers and can turn their heads in a way that mimics human movement, reinforcing the illusion of a mermaid.^19-21 Given the prolonged nature of sea voyages,²² combined with the toxic effects of stimulants²³ and the deprivation of essential nutrients, it is likely that these factors contributed significantly to the sailors’ misidentifications, enhancing the illusion of mermaids.

Conclusion

Alcohol, opium, and tobacco, in combination with psychological and environmental stressors, have likely contributed to hallucinatory mermaid sightings. While mermaid sightings are often dismissed as folklore, they provide insight into the complex interplay between human physiology, cultural narratives, and the limits of perception. Future research could explore historical ship logs for further evidence of hallucinations among sailors and the role of nutritional deficiencies in cognitive distortions.

References

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