Have you got a current driving licence? thyroid medication levothyroxine dosage A study by Halfords also revealed that 10 per cent of drivers suffering from hay fever - which could equate to more than a million motorists - said they have been affected so badly that they have had to stop the car until the sneezing subsided. And, almost a third of drivers who suffer from hay fever admitted they had taken their eyes off the road while searching for tissues.