Seasickness: pills, the scopolamine patch and prevention

Seasickness is a form of motion sickness. It happens when what your inner ear feels doesn't match what your eyes see: the boat is moving, but you are looking at something that seems still, like your phone or a cabin wall.

In Puerto Rico it hits a lot of people on the ferries from Ceiba to Culebra and Vieques, on day-trip catamarans and on cruises calling at San Juan. If you feel dizzy on dry land, with no boat involved, see dizziness; the doctor can evaluate that by video too. And if you have nausea with no motion involved, see that guide.

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According to the CDC and MedlinePlus, motion sickness can start suddenly with:

• A queasy stomach and nausea
• Vomiting
• Cold sweats
• Dizziness
• Drowsiness or tiredness

The CDC says motion-sickness medicine works best when taken before you are exposed to motion. The most common motion sickness pills are antihistamines sold over the counter in the United States and Puerto Rico. The CDC's figures for when each one starts working:

• Dimenhydrinate: starts in about 2 hours and lasts about 8 hours.
• Meclizine: starts in about 2 hours and lasts about 8 hours; the over-the-counter chewable tablet can last 8 to 24 hours.

They cause drowsiness and a dry mouth, so don't drive after taking one or mix it with alcohol. Read the label and ask your pharmacist if you take other medicines, are pregnant or are buying it for a child.

The scopolamine patch is a prescription medicine useful for long trips such as a cruise. According to MedlinePlus, it goes on the hairless skin behind your ear at least 4 hours before you need it and can stay on for up to 3 days; the CDC says it reaches its effect 6 to 8 hours after you put it on. Wash your hands well with soap and water after touching it.

It is not for everyone. It is not used with angle-closure glaucoma or if you have trouble urinating because of your prostate, it is avoided in children because it can cause confusion or hallucinations, and MedlinePlus says older adults should not usually use it because it is not as safe for them. If you get confused, have eye pain or redness, blurred vision, or your body temperature rises or you sweat less, take it off and get medical care.

The doctor decides what is appropriate for you; we never promise a specific medicine. If appropriate, the doctor prescribes and we send your prescription to your pharmacy. Pick it up before you head to the dock: see 24-hour pharmacies in Puerto Rico, because the pharmacy counter isn't always open when the store is. On a cruise, also read the cruise passenger guide.

According to the CDC, getting used to the motion works best of all, better than medicine. Also:

The CDC advises starting with the non-medicine measures and avoiding scopolamine patches in children, because they can cause confusion or hallucinations. Ask before giving a child any motion-sickness medicine; we see children of all ages with their parent or legal guardian on camera.

Seasickness fades soon after you are back on land. If vomiting won't stop and you can't keep fluids down for hours, you can get dehydrated: read about dehydration.

Call 911 if dizziness comes with chest pain, shortness of breath, palpitations, weakness on one side, a drooping face, trouble speaking or vision loss. On a cruise, tell the ship's medical center first; see the cruise passenger guide.