Answer
Seek assessment if it persists, rapidly worsens, produces substantial phlegm, or occurs with chest pain, breathing difficulty, coughing up blood or feeling very unwell.
Sources for this answer
- Benylin Dry Coughs 7.5mg / 5ml Syrup — Current selected SmPCemc · Summary of Product Characteristics
- NHSNHS · NHS medicine guidance
General medicine information. Follow the instructions for your own medicine and speak to a pharmacist or clinician about your individual circumstances.