Singapore banned the sale of chewing gum in 1992 — with exceptions for medical and dental gum
Singapore's 1992 Chewing Gum Ban was motivated by maintenance issues: gum was being stuck in MRT train door sensors, causing door malfunctions and service disruptions. The ban covers the import and sale of gum (not the chewing of it by residents who have sourced it elsewhere). Medical gum such as nicotine gum and dental gum are available by prescription. The ban was internationally mocked but MRT service reliability improved measurably. Singapore's approach was characteristically pragmatic.
One of the most effective public transport systems in the world banned an entire consumer product because of door sensors. And it worked.
“Singapore banned chewing gum in 1992 because it kept jamming the MRT train doors. The ban improved train reliability.”