Guaifenesin appears to be one of the safer additional ingredients to take in excessive doses along with the DXM. However, it is still recommended that you find a DXM source free from other actives, since you're increasing your risk of serious complications with no additional phsychotropic effects. If you absolutely MUST use this particular formulation, be sure to drink plenty of fluids both during and after the experience, since guaifenesin has a drying effect, especially in the lungs.