Call, or have someone call 911 immediately. DO NOT try and provide any care to the individual prior to making this call. If you have NARCAN* administer it immediately after the 911 call has been made. If the person is not breathing, and you are certified in CPR, begin the process of life saving measures until emergency services have arrived or the individual has begun breathing on their own.
*NARCAN, also known as naloxone, is a life saving medicine that can reverse the effects of an opioid overdose. It can be obtained over the counter at most local pharmacies.