Answer
Yes. A guaifenesin metabolite can interfere with some urinary 5-HIAA and VMA tests. Tell the requesting clinician and laboratory that you have taken it.
Sources for this answer
- Benylin Mucus Cough Night — Current selected SmPCemc · Summary of Product Characteristics
General medicine information. Follow the instructions for your own medicine and speak to a pharmacist or clinician about your individual circumstances.