Honey is very sweet because it has a high sugar content.
The affect this may have on your BG is dependent on many things such as how much you take, what you take it with and, quite simply, how your body handles it: we are all different.
The best way to find out if you can take honey without a significant BG rise is to try it: test your BG, take the honey and then test again after 2 hours. If your BG has not risen more a couple of mmol/l, honey is ok for you.
Alternatively, there are some sugar-free cough medicines available which should have limited impact on your BG.