One in five NSW families are doping their children with medication to keep them quiet on long road trips, a new national study of motorists has revealed.

The driving survey, commissioned by insurer GIO, shone a light on the behaviour of 3700 parents, including 600 within NSW, who embark on extended road journeys.

Orlando Moodley, 3, enjoys watching Ice Age on a DVD player while his dad Paul concentrates on driving. Credit:James Alcock

While four in five families give youngsters hand-held computer games, including iPads, and 70 per cent keep treats up their sleeve, 18 per cent of NSW drivers admit to tranquillising their children with drugs that sedate - such as the antihistamine Phenergan - to make the journey more comfortable.

The drug is available over the counter and is commonly used in the treatment of allergies. Phenergan is the product name given to the drug Promethazine. According to patient inforrmation guides, compiled by its various manufacturers, Phenergan should not be used on children aged under two, due to its potential for "fatal respiratory depression".