The green response bag was reported missing from the West Lothian vehicle at 6am today (Mon) but is believed to have been taken sometime between Sunday night and the early hours of this morning.
Officials suspect the theft was made when paramedics attended a call in Townhead Gardens, Whitburn around 2.50am.
The bag contained some items of medication, along with syringes and hypodermic needles, and police are concerned these could cause harm if not taken as prescribed.
A police spokesman said: “None of the medication in the bag is believed to be particularly harmful, but as with all medicine it could be dangerous if taken in high doses, without a prescription.
“We would ask anyone who might find the green response bag to hand it in to the nearest police station or medical centre.
“At the same time, we are appealing to anyone who may have been in the area of Townhead Gardens in the early hours of this morning, who witnessed the bag being removed from the ambulance, to contact police.”