Vancouver police are warning drug users about the potential for accidental overdoses after the theft of various drugs including fentanyl from a pharmacy.

Police say a gun was used during the robbery, and that health officials are concerned about the risks of people using fentanyl in particular.

The synthetic narcotic is 50 to 100 times more toxic than other opioids and the dose must be carefully monitored to prevent overdose.

Early signs of a fentanyl overdose include severe sleepiness, trouble breathing, cold, clammy skin and trouble walking or talking.

Police are advising drug users to never inject, snort or swallow drugs alone and to call 911 immediately if overdose symptoms start.

Provincial health officer Dr. Perry Kendall recently said about 25 per cent of fatal overdoses in B.C. last year resulted from the use of fentanyl.