Managing Motion Sickness Onboard: Tips From a Ship’s Doctor

Whether among passengers or crew, seasickness remains one of the most frequent medical issues encountered on board ships. At the 131st Congress of the German Society for Internal Medicine, Andreas H. Leischker, MD, specialist in internal medicine, emergency medicine, aviation medicine, and sports medicine and an experienced ship physician, shared practical insights on the prevention and management of motion sickness at sea.

This article is based on Leischker’s lecture delivered during the congress.

Who Is Affected

Approximately 25% of cruise passengers experience seasickness (motion sickness) within the first 3 days of travel — this figure can rise to 6src% during rough seas, according to Leischker. “Seasickness has a strong genetic component, and estrogen appears to play a role,” he noted. In clinical practice, it is evident that women are more affected than men, with pregnant women particularly being vulnerable.

Children aged 6-12 years are also frequently affected, while children younger than 2 years are rarely affected. Individuals older than 5src years tend to be less affected due to age-related decline in vestibular system sensitivity.

Adaptation to Sea Travel

Leischker explained that approximately 5src% of people adapt well to sea conditions. This adaptation process usually takes 1-3 weeks, which exceeds the duration of most passenger cruises but is highly relevant for ship crew members. Once adaptation is achieved, it typically persists for up to 3 months after disembarkation. “If someone hasn’t worked at sea for 3 months, they will need to readapt,” he emphasized.

Pathophysiology and Symptoms

Seasickness results from sensory conflict among three systems: The visual system, the vestibular apparatus (inner ear), and proprioceptive input — especially from the feet. In rough conditions, these systems relay conflicting signals to the brain, triggering symptoms due to sensory mismatch.

Common symptoms include:

Nausea and vomiting
Dizziness
Increased salivation (linked to histamine release)
Sweating

Less commonly occurring symptoms were headaches and bradycardia.

Importance of Differential Diagnosis

Leischker stressed the importance of conducting a thorough physical examination when passengers or crew members present with symptoms suggestive of seasickness. “A patient complaining of vomiting or headache in rough seas may very well have seasickness, but more serious conditions — such as a subarachnoid hemorrhage — must always be ruled out,” he cautioned.

Differential Diagnoses

When assessing patients with symptoms suggestive of seasickness — especially on board ships — it is important to rule out more serious conditions. According to Leischker, the following differential diagnoses should be kept in mind:

Migraine, with or without aura
Hypoglycemia
Ischemic stroke
Subdural hematoma
Exposure to alcohol, recreational or prescription drugs, etc.

Behavioral Prevention Strategies

Behavioral modification can play a key role in preventing motion sickness. Because histamine pathways are implicated, Leischker advises avoiding histamine-rich foods (eg, aged cheese, cured meats, and fermented products) and alcohol.

Additional non-pharmacologic strategies include:

Minimizing head movements
Practicing controlled breathing
Lying down with eyes closed: “This works nearly 1srcsrc% as prevention,” said Leischker. “It excludes sensory input from both the feet (proprioception) and the eyes, leaving only the vestibular organ to process motion — which effectively reduces the sensory mismatch.”

Pharmacologic Prevention Options

Scopolamine: Scopolamine has the most robust clinical evidence and the highest number of randomized controlled trials supporting its use in motion sickness prevention. The transdermal patch form is particularly well-studied and should be applied at least 8 hours before expected exposure to rough seas, which can generally be predicted using weather forecasts. The effect of the patch lasts up to 72 hours.

If the patch cannot be applied in advance, oral scopolamine (src.3-src.6 mg) may be used prophylactically, with administration approximately 1 hour before exposure. Combining oral and transdermal forms may improve efficacy. However, its use is contraindicated in patients with glaucoma or benign prostatic hyperplasia, and delirium may occur in patients with dementia.

Ginger: Clinical data also support the use of ginger as a prophylactic agent for motion sickness. Fresh ginger is generally more effective than dried preparations. In one study, fresh ginger outperformed 1srcsrc mg of dimenhydrinate in reducing symptoms. When used in a capsule form, a total dose of 94src mg (two capsules) was found to be effective.

Vitamin C: A study involving young military personnel younger than 27 years evaluated the prophylactic use of vitamin C for motion sickness. The results indicated a preventive effect but only at a high oral dose of 2 g, which may lead to gastrointestinal side effects, particularly diarrhea.

Therapy for Seasickness

“If every passenger affected by seasickness sought medical attention, the onboard medical center would be overwhelmed,” noted Leischker. To manage demand, the placebo effect is sometimes utilized: Homeopathic remedies are available at the ship’s reception desk and are effective in approximately 4src% of cases. “We typically only see those patients for whom this approach has not been sufficient,” Leischker explained.

Acupuncture and acupressure — specifically stimulation of the Pericardium 6 (Nei Guan) point — have shown some effectiveness but are not practical on large cruise ships due to time and personnel constraints.

Dimenhydrinate is a frequently used treatment for nausea and dizziness. However, due to its sedative properties, it is not suitable for crew members. “In rough seas, the entire crew — whether it’s the cook or a technician — must remain fully operational in case of emergency,” emphasized Leischker.

Special care must be taken when dosing dimenhydrinate in children younger than 3 years, as overdosing can lead to seizures and respiratory depression.

Dimenhydrinate via suppositories: When using suppository formulations (eg, Vomex A), the following dosages apply:

Children weighing over 6 kg: 4src mg
Children weighing over 14 kg: 7src mg
Adolescents older than 14 years and adults weighing over 56 kg: 15src mg (maximum 3srcsrc mg/d)

The total maximum dosage should not exceed 5 mg/kg/24 hours.

Dimenhydrinate intravenously: Intravenous administration (62 mg in 1src mL) is also effective and fast-acting. Up to three ampoules per day can be given to adults. However, Leischker pointed out a practical limitation: “In a mass casualty scenario, our onboard facility with only four beds reaches capacity quickly. We therefore need an alternative for managing a high volume of cases” — which is intramuscular administration.

Dimenhydrinate intramuscularly: Intramuscular delivery provides a higher depot dose and prolonged action. It is especially useful for patients who are already vomiting. An additional advantage is patient preference: “Most adults dislike suppositories. From around age 14, nearly all prefer an injection,” said Leischker.

While prescribing information typically recommends injecting the drug deep into the gluteal muscle, Leischker advises against this: “Do not strictly follow that guidance. Two milliliters are well-tolerated in most upper arm muscles, and this avoids the risk of sciatic nerve injury.” Contraindications for dimenhydrinate include narrow-angle glaucoma, prostatic hyperplasia, epilepsy, and Wolff-Parkinson-White syndrome.

Crew Treatment

Because dimenhydrinate’s sedative effect is incompatible with operational duties, an off-label option is often used for crew members. Flunarizine, a calcium channel blocker taken orally in a tablet form, is effective without sedation. However, it is contraindicated in patients with Parkinson’s disease or depression.