The study of 1,012 patients collecting a sulphonylurea prescription from a pharmacy found 38% were unaware of the side effects of their treatment.
Half had suffered a hypoglycaemic event yet just 38% had reported these incidents to their GP.
Only 3% of patients said they checked their glucose levels before driving. The DVLA attributes 45 serious events each month and five fatal crashes a year to hypoglycaemia.
The research, funded by drug company MSD, was presented at the Diabetes UK Professional Conference 2013 last week.
Study co-author and Kent GP Dr Richard Brice said: 'This highlights the worrying unawareness of hypoglycaemia as a serious issue.'
He said GPs and other health professionals must do more to educate patients about the importance of avoiding hypoglycaemia, especially when driving.
Surrey GP Dr Neil Munro, member of Primary Care Diabetes Society (PCDS), told GP: 'Hypoglycaemia is under-reported because patients are often not aware of the symptoms and health professionals do not specifically ask about hypoglycaemia.'
Yet he said the symptom could lead to significant occupational risks. 'In addition severe hypoglycaemia on sulphonylureas can lead to loss of a driving license,' he said.
Warwickshire GP Professor Roger Gadsby of the University of Warwick and PCDS founder said: 'It is vital that people are aware of side effects of medications and tell their GP about them so that discussion can take place about whether a change of medication is necessary.'