SEASICKNESS

Photo provided by Professor Hugh Grantham

Seasickness has been around for as long as humans have gone to sea. There are numerous expert explanations as to what causes it and why some people suffer more than others. Declaring a conflict of interest, I suffer from it, and I spend a lot of time treating it. The more I learn about it, the more I realise how much we still don’t understand. Some motions are worse than others, going below deck seems to make it worse, and certain smells can trigger it. Fatigue and stress also appear to be contributing factors.

If we accept the generally held view that seasickness is related to conflicting information about balance and other sensory inputs in the brain, it helps explain why lying in a bunk with your eyes closed can be beneficial. It also fits with the observation that focusing on the horizon or steering the boat helps. However, it does not explain the 20-minute “honeymoon period” following vomiting. Beyond these observations, the precise mechanics of vomiting—aside from its role as a protective mechanism against ingesting poisons—are less clear than many “experts” claim.

What works?

With your permission, I’ll skip past magnets, ginger, and pressure points. Some medications do help.

Hyoscine

This is the main ingredient in many over-the-counter seasickness tablets. It works by blocking the parasympathetic nervous system, which among other things controls gut motility. Interestingly, it doesn’t penetrate the brain well. Side effects can include a dry mouth, mild drowsiness in some people, and bladder obstruction in those with an enlarged prostate. Some over-the-counter products contain only hyoscine, while others combine it with antihistamines and caffeine.

Antihistamines

Modern antihistamines are much less sedating than older ones and generally have fewer side effects. Many chemist-brand seasickness tablets combine a modern antihistamine with hyoscine. In addition to their role in treating allergies, antihistamines also seem helpful in managing motion-induced nausea.

One old-fashioned, sedating antihistamine still in use is promethazine hydrochloride, sold as Phenergan. It is very sedating and not ideal for someone who needs to remain alert. Side effects include sedation, sleep disturbances, hallucinations, and even psychosis. It now carries an official government TGA warning against use in young children, despite having been used for that purpose in the past. In my opinion, this is a drug of absolute last resort.

Caffeine

The other component often found in over-the-counter medication is caffeine, also commonly obtained from your local café. It is a central nervous system stimulant and is not known to have an anti-nausea effect on its own. Presumably, it is included to counteract the sedative effects of the other drugs.

Pre-treatment

These preventative treatments work best if taken the night before sailing and continued two or three times a day for the first two to three days until you’ve found your sea legs. If the weather turns rough, it’s worth restarting them for a short period.

Scopolamine

Previously available as skin patches and still obtainable in some parts of the world, scopolamine is closely related to hyoscine and acts in a similar way.

Ondansetron

Available by prescription, this is a newer anti-nausea medication originally developed for chemotherapy-induced nausea. It acts on a completely different neurotransmitter (serotonin) and appears to work even after seasickness has started. The sublingual form (absorbed in the mouth rather than swallowed) works quickest, usually within about 35 minutes. It is also available as an injection, which cannot be vomited up—an advantage in severe cases.

Prochlorperazine (Stemetil)

An older injectable anti-nausea medication that acts on yet another neurotransmitter (dopamine). It can break the cycle of vomiting and often turns a persistent problem around.  It is also available as tablets, but probably offers no advantages over the other tablets already mentioned. A small number of people experience central nervous system side effects, so it should not be used lightly.

There are other drugs that may be considered, and intravenous fluid resuscitation may be necessary if you are fortunate enough to have a medical officer on board.

Tough it out vs treat it?

There remains a school of thought that you should simply endure seasickness and wait to get your sea legs in two to three days. In the past, when treatment options were limited, this was often the only choice. That is no longer the case.

Treating seasickness does not slow the adaptation process—you’ll still get your sea legs at the same time. So why suffer unnecessarily? Seasickness consumes mental bandwidth, makes you less functional, less able to learn, and is frankly miserable.

Kidney failure

Severe seasickness can lead to dehydration, especially if the person is unable to keep fluids down. This can lead to renal (kidney) failure. The risk increases if the individual is taking anti-inflammatory drugs like ibuprofen (Nurofen) or certain blood pressure medications. Someone who has not passed urine in 12–24 hours and cannot keep fluids down is at serious risk and requires active treatment. Risking kidney failure is unacceptable—quite apart from being inhumane—when there are effective alternatives.

Final comments

·        We don’t understand seasickness as well as some claim.

·        Preventative treatments may not eliminate seasickness but usually reduce its severity, so they are worth persisting with.

·        The old “tough it out” mindset is outdated and risks real harm—including kidney damage—and deters people from sailing.

·        Treating seasickness does not slow the process of gaining your sea legs.

By Professor Hugh Grantham - Chair of Emergency Medicine Foundation - Australasia (EMF), Chair of One and All tall ship board and Professor adjunct QUT (Queensland University of Technology) and Curtin University. He is one of the editors of Australian Boating Manual 6th edition.

Have you ever experienced seasickness? We'd love to hear your stories and thoughts - share them in the comments!