Car, boat, plane — the moment it starts, the only thing on your mind is making it stop.
Dimenhydrinate interrupts the signal between your balance organ and the part of the brain that triggers vomiting.
Without prescription, plain packaging. Timing is everything here, and it causes drowsiness.
It comes down to your brain getting two stories that do not match.
Your inner ear registers movement — acceleration, swaying, turning. Your eyes, fixed on a book or the inside of a cabin, report that nothing is moving. Your joints and muscles chip in with their own version.
The brain cannot reconcile the three. And one of its older responses to confusing sensory input is to assume poisoning, which means getting rid of whatever is in the stomach.
Crude, but that realy is the mechanism. It also explains why looking at the horizon helps: it restores agreement between eyes and inner ear.
How the tablet interrupts it
Dimenhydrinate blocks histamine receptors along the pathway running from the balance organ to the vomiting centre in the brainstem.
It also has an anticholinergic effect, which damps the same pathway from a second angle. That is why it works on vertigo as well as travel, and it is also the source of the dry mouth.
The signal still arrives. It just arrives weaker, and below the threshold that would set off nausea.
Why is timing the whole game?
Here is where most people lose.
Once nausea has properly started, the stomach largely stops emptying. A tablet swallowed at that point sits there instead of being absorbed, and it works badly or not at all.
Take it half an hour to an hour before setting off. On a long journey, repeat at the interval on the pack rather than waiting to feel ill again.
If you already feel sick, it may still help, just slower and less reliably. Prevention is a different league from rescue here.
Will it make you drowsy?
Not a maybe. Drowsiness is the main side effect, and for a passenger on a long crossing it is sometimes welcome.
For a driver it is a problem. Do not drive after taking this. Do not operate machinery either, and avoid alcohol, which stacks on top of it.
The effect can still be around the next morning after an evening dose. People underestimate that.
Other things that help, with or without the tablet
Sit where there is least movement — front seat, over the wing, midships on a boat
Look at the horizon, not at a screen or a book
Fresh air on your face
Eat something light beforehand; neither stuffed nor empty
Keep your head still against a headrest
Skip alcohol the night before
Reading in a moving vehicle is the fastest way to bring it on, because it maximises the disagreement between eyes and inner ear.
Beyond travel
It is also used for nausea and vomiting from other causes, and for vertigo from inner ear problems.
One caution with vertigo: it suppresses the symptom, and if used for weeks it can slow down the brain's own adjustment to an inner ear problem. Short course, not a long-term fix.
Who should be careful
Glaucoma, the narrow-angle type
Enlarged prostate or difficulty passing urine
Epilepsy
Severe heart or liver disease
Asthma
Older adults, who are more sensitive to confusion and falls
Anyone already taking sedatives, strong painkillers or alcohol
Possible side effects
Drowsiness, the common one
Dry mouth
Blurred vision
Constipation
Difficulty passing urine
Confusion, mainly in older people
Occasionally restlessness instead of sedation, particulary in children
That last one reads like a mistake but it is real. A minority react the opposite way and become agitated.
When nausea needs looking at
Vomiting that will not stop, blood in it, severe abdominal pain, a bad headache with a stiff neck, or vertigo with hearing loss or double vision. None of those are travel sickness.
Ordering without prescription: how it works
This one belongs in the bag before the trip, not bought at an airport at the last minute.
Pick the strength and the pack size, put in a delivery address, confirm. Couple of minutes, any time of day, no queue and no conversation across a counter.
It goes out in plain packaging. No pharmacy name on the outside, nothing that hints at what is inside. How long delivery takes depends on where the parcel is headed.
On price it comes down to strength and pack size. Larger packs generally work out better per unit, and over a long season that gap adds up.
If something arrives damaged anywhere in the UK, send the order number and a photograph the same day. We replace free of charge or refund in pounds. Do not use medication from a damaged blister.