Answer
Very rare serious hypersensitivity reactions reported with Benylin Herbal Cough & Cold Sugar Free Syrup involved facial swelling, dyspnoea (difficulty breathing) and decreased blood pressure.
Sources for this answer
- Benylin Herbal Cough & Cold Sugar Free SyrupMcNeil Products Ltd · emc · SmPC §4.8 Undesirable effects · Version 1Document updated
Sources checked