My Fiance Has Been Taking Mucinex For Severe Cough For

my fiance has been taking mucinex for severe cough for 7 years. He eats them like candy. He is 49, 5'11" and 205 pounds. He has been having trouble having or keeping an errection for the past 3-4 years. He has avoided my concerns and constant questioning until just this weekend he said he was doing research and thinks perhaps the ingredient in mucinex, guaifenesin could be the problem. Is this really a possibility?