Does guaifenesin cause nosebleeds?

Unfortunately, you are not alone! I had an uncontrollable nosebleed after starting Benylin (Guaifenesin) for cough last night. It is a well guarded secret as hundreds of people are reporting haemorrhaging as a side effect on the internet and yet it is not included in any textbook, medical reference etc. And it is definitely not on the label! Sincere hopes that it didn’t affect you otherwise as it could cause internal bleeding or brain haemorrhage (insult).

Nosebleeds is not a known side effect of guaifenesin but since it started once you started taking guaifenesin there may be a link.

https://www.drugs.com/sfx/guaifenesin-side-effects.html