I wouldn't use it. I used it with DS1 once and never again. I used a suppressant and it did suppress the cough, which in turn made it last longer as the idea of coughing is to cough up the nasties! In turn it made the junk stay in his chest and he ended up with an infection. It also made him wheeze (before the infection kicked in) so that just made matters worse. That was a long time ago when cough medicine seemed to be the 'done thing'
Check out Michelle71's link, and there's lots more around too if you're interested. Steam is good,as some of the other posters have mentioned lots of water and cuddles
I hope your bubba feels better soon.