i don't know if anyone has had a problem taking robitussin dm, but i sure did! i took it every 4 hours as directed on the bottle one day and could not sleep and had a horrible headache all night and the next day. this is the first time that i took it in this fashion. i have had a bad cough for awhile and have been on several antibotics with not much success. is this a normal side affect? i will not take anymore of that cough medicine again. is there anything that someone can suggest for a cough?