Travel sickness tablets are taken before you set off, not once you already feel ill. With dimenhydrinate, the first dose should be at least half an hour before the journey starts, and preferably one to two hours before. That margin isn’t a convenience: it is the time the medicine needs to be absorbed and reach the brain.
And there is a physiological reason not to leave it until later. Once motion sickness symptoms begin, gastric stasis sets in: the stomach stops emptying normally. A tablet taken at that point may not absorb properly even if you don’t actually vomit. Which is why the useful window is before you get in the car, not at the side of the road.
Why it happens
Motion sickness is best explained by the theory of sensory conflict. Your brain builds an expectation of how the body should be moving by combining three sources: the inner ear, your eyes, and information from muscles and joints. When those signals don’t match each other, or don’t match what the brain expected, the centres that produce nausea and vomiting fire.
The classic example is the back seat with a phone in your hand: your inner ear picks up acceleration and bends, but your eyes are fixed on a stationary screen. That is the mismatch. Everything that works without medication essentially consists of reducing it.
Symptoms don’t start with vomiting. They usually progress from something much subtler: an odd feeling in the stomach, warmth, yawning, cold sweat and pallor, dizziness, and only then nausea and vomiting. If you recognise the early signs, there is still time to act.
Who gets it worse
- Age is the main factor. Under-2s barely get motion sick at all. Susceptibility rises afterwards, peaks between 7 and 12 years, and declines through adult life, probably through habituation.
- Genetics count for a lot. Twin studies attribute between 55% and 70% of individual variation to inherited factors.
- Migraine and vestibular disorders predispose you: anyone with a history of migraine or vertigo gets motion sick more easily.
- Too little sleep makes it worse. So do alcohol and nicotine, which means the night before counts.
What works without medication
| Measure | What it does | Limitation |
|---|---|---|
| Habituation | The single most effective measure, more so than any drug, and with no side effects | Builds slowly and tends to be specific to the stimulus |
| Looking at the horizon | Reduces the conflict between eyes and inner ear | Impossible below deck or with no window |
| No reading or screens | Effective in cars, boats and simulators | Rules out reading maps or working |
| Keeping the head still | Reduces the vestibular stimulus | Uncomfortable on long journeys |
| Lying down | Works mainly because it limits head movement | Not always possible |
| Leaning into the bend | Aligns the body with the vehicle’s forces; on a boat this is what “getting your sea legs” means | Requires anticipating the movement |
| Choosing your seat | On a plane, near the wings; on a boat, avoid the bow | You can’t always choose |
| Driving yourself | Feeling in control of the vehicle reduces sickness | No use as a passenger |
| Controlled breathing | Breathing at a steady rhythm; in the lab it delivers half the benefit of a drug, with no adverse effects | Takes practice and attention |
Apart from habituation, all of these are only partly effective. Combining them pays off more than relying on one.
The medicines: which and when
In Spain the usual over-the-counter active ingredient is dimenhydrinate, an H1 antihistamine acting centrally. It comes both on its own and combined with caffeine.
Dimenhydrinate 50 mg. In adults and over-12s, 1 or 2 tablets (50-100 mg) per dose; if needed it can be repeated every 4-6 hours, without exceeding 8 tablets (400 mg) a day. Taking it with food, water or milk is recommended to reduce stomach irritation. The effect starts at around 2 hours and lasts about 8. Get advice if you get worse or if symptoms persist beyond 7 days.
Dimenhydrinate with caffeine (50/50 mg). The caffeine is there to counteract drowsiness. The regimen in adults and over-12s is the same — 1 or 2 tablets, repeatable every 4-6 hours, maximum 8 a day — but the last dose shouldn’t fall within 6 hours of bedtime, to avoid insomnia. This version adds caffeine’s own contraindications: high blood pressure, anxiety or insomnia, peptic ulcer, serious liver or heart conditions. It is not for under-12s.
Be careful in these situations. Dimenhydrinate should not be taken if you are allergic to the active ingredient or to diphenhydramine, or if you have porphyria or are having an asthma attack. Check first if you have glaucoma, an enlarged prostate, an overactive thyroid, epilepsy, asthma or COPD, urinary or digestive obstruction, heart, liver or kidney disease, ulcer or gastritis, or if you are over 65. It can also mask the symptoms of appendicitis and the signs of toxicity from drugs that damage hearing.
Two practical warnings that always get forgotten: don’t drive or operate machinery while taking it, because it causes drowsiness and slows reaction times; don’t mix it with alcohol; and avoid sun and UV exposure, because it can cause photosensitivity. If you are due to have skin allergy testing, it has to be stopped 72 hours beforehand.
In children, try the non-drug measures first. There are presentations and regimens by age band, but let the pharmacist or paediatrician specify them, rather than splitting an adult tablet by eye.
For long, intense exposure — a rough crossing — there are alternatives such as the scopolamine patch, which requires a prescription in Spain. If you are going to need one, that is a conversation to have before travelling, not at the harbour.
Three very common mistakes
- Using your hay fever antihistamine. Cetirizine, loratadine or fexofenadine don’t work for motion sickness. They are designed specifically not to enter the brain, and that central effect is exactly what is needed here.
- Counting on acupressure wristbands. Laboratory trials don’t find them more effective than placebo. If they work for you, the placebo effect can be powerful and there’s no harm in using them, but don’t take them as your only plan.
- Trusting ginger and assorted supplements. The evidence on diets, vitamins and ginger is weak and contradictory. Other distractions — fresh air on the face, music, pleasant smells — at least have the advantage of promising nothing.
When to see a doctor
Seek medical assessment if:
- The dizziness appears with no movement involved, or hits you while sitting still at home.
- It comes with hearing loss, ringing in the ear or a blocked-ear sensation.
- There is double vision, difficulty speaking, weakness down one side, facial numbness or unsteadiness on your feet: that is not motion sickness and needs urgent attention.
- The headache is severe and different from the ones you usually get.
- Vomiting stops you keeping fluids down, particularly in children or older people, because of the dehydration risk.
- The swaying sensation persists for days or weeks after getting off the boat.
- Symptoms don’t improve or get worse after 7 days of treatment.
- You take long-term medication, have glaucoma, prostate problems, epilepsy, arrhythmias or liver disease, or are pregnant or breastfeeding: check before taking anything.
This information is general and does not replace assessment by a healthcare professional. Sources consulted: AEMPS/CIMA — Patient leaflet, Biodramina 50 mg tablets (dimenhydrinate, in Spanish), AEMPS/CIMA — Patient leaflet, Dimenhidrinato/Cafeína Gobens 50 mg/50 mg film-coated tablets (in Spanish) and CDC Yellow Book 2026 — Motion Sickness (J. F. Golding).