Fortunately, the homeopathic remedies Petroleum, Tabacum or Cocculus can all help with this problem, and avoid the side effects of drowsiness dry mouth that you might notice from conventional motion sickness treatments. Homeopathic remedies are free from toxic side-effects, and are safe for all ages.
Homeopathy works best when remedies are specially selected to match the individual patient and their particular symptoms, so the choice of which remedy is right for your motion sickness depends on how you experience your particular motion sickness symptoms.
For example, if you get a deathly nausea with a terrible faint, sinking feeling in the stomach and you feel as though you want your abdomen uncovered, you could try a few doses of Tabacum 6c or 30c, stopping on improvement.
Professional homeopaths study for a fair few years to learn how to choose the correct remedy for each individual, so your local homeopath can help you to choose the right remedy for you. Alternatively, there are homeopaths like me who have an international client base, treating via phone, email or Skype.
If you prefer to treat yourself, but you don't fancy reading up on the remedies to find out which would suit you best, you could try this one-size-fits-most combination: Cocculus indicus 30c + Petroleum 6c + Tabacum 6c.
A good homeopathic pharmacy can make this up for you, or it should be available from any good homeopath.
For a prolonged trip, start taking this two days before travelling, and take three times daily until the trip is over. For a short trip, such as a day's outing, start the remedyat least an hour before you go in the car, and take every 15-30 minutes as needed through the journey. In either scenario, stop taking the remedy as soon as you feel that it's working: with homeopathy, less is more!
One non-homeopathic common sense precaution that is worth following is to ensure that you avoid heavy or greasy meals before the journey.
I hope this information is helpful, and do contact me, or your local professional homeopath, if you need more advice. Disclaimer: Any views or advice in this comment should not be taken as a substitute for medical advice, diagnosis or treatment, especially if you know you have a specific health complaint. Prescribed medication should not be stopped or varied without conventional medical advice. Please remember that homeopathic remedies and other health measures should be individually-selected to match the whole person, not just the unwelcome symptom. Seek professional advice rather than self-prescribing if your complaint is chronic, severe or long-standing, or if you are pregnant, elderly or on orthodox medications.