As he is now 6 months(+) old I agree that it may be time to seek the aid of drugs in providing some relief from the car sickness to avoid a negative association with the vehicle itself. Speak to your vet.
My pup experienced/experiences car sickness as well although with time it is slowly subsiding.
Her initial symptom was vomiting followed by excessive (soaking the car seat) salivation due to a stress reaction even upon be seated in the vehicle without motion. (I have been told
not to touch the puppy while they are under this amount of stress.)
After about her third ride she stopped salivating but avoided looking out of the window and would curl up into a ball in the front seat.
Finally after a little over a month of short drives she has started to remain seated and explore the sounds and sights outside of an open window. On the longer drives she will curl up into a ball and lye down. With time I expect her to overcome the sickness altogether.
Similar to what babies experience in an airplane, at a young age their ossicles are still developing and so it is natural for them to experience some car/motion sickness. For the puppy it is typically the motion of other vehicles which causes the motion sickness.
It may take up to a year for development of the inner ears at which point I have been told the motion sickness completely subsides barring any prolonged negative associations.
What has been the progression of your puppy's symptoms?
Have you noticed any improvement with time or different positions in the car?
If not you may have reached the point at which you experiment with drugs similar to
@lhczth 's suggestion in order to break the cycle.
The drugs most certainly are not anything to be afraid of with regards to side effects and they work by inhibiting receptors responsible for the sickness. These drugs are very effective and better to experiment with than allowing the stress your puppy may be currently experiencing with the ride,
most notably that stress prior to a training session cannot be good for your pup.
Some precautions I take to avoid car/motion sickness:
- Start with short drives and gradually work up to the more lengthy drives
- Slightly open windows on both sides to maintain an equilibrium of pressure in the vehicle
- Avoid feeding at least 1 hour prior to the ride
- Drive slow and carefully avoiding sudden stops and bumps. The front of the vehicle will be best to minimize the amount of motion he experiences.
- I give a bit of sugar prior to the drive to help as a physiological prevention to the motion sickness.
