Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
1
Is any of this happening now?
Call 911
Call emergency services if someone has:
Trouble breathing, blue or grey lips, or very slow breathing
A seizure, collapse, or inability to wake
Chest pain, severe shortness of breath, or fainting
Extreme agitation, violent behaviour, or immediate risk of self-harm
New weakness, severe headache, or other possible stroke symptoms
A serious injury or possible exposure to opioids or another unknown drug
Other emergency signs, for anyone
Someone who is struggling to breathe, gasping, choking, or cannot get words out
Someone who has chest pain, tightness or pressure lasting more than a few minutes
Someone who has sudden weakness or drooping on one side of the face or body, slurred speech, or sudden confusion
Someone who is unconscious, or cannot be woken
Someone who is bleeding heavily and it will not stop with firm pressure
Someone who has had a seizure that will not stop, or does not wake up afterwards
Someone who has lips or skin that look pale, blue, grey or blotchy
Someone who you believe has taken an overdose or swallowed something poisonous
2
Is any of this happening?
Be seen today
Contact a poison centre promptly if a child may have eaten or drunk a cannabis product, even if symptoms have not appeared.
Also seek urgent advice for a pregnant person, an older or medically frail adult, or anyone who took an unknown amount or an unidentified product.
3
Does any of this apply?
Book an appointment
Routine medical follow-up is appropriate if anxiety, suspicious thoughts, poor concentration, or vomiting continues after the expected effects should have passed.
Follow-up can also help if intoxication is happening repeatedly or cannabis use is becoming difficult to control.
The article also says
Place an unconscious but breathing person on their side if it is safe to do so.
Do not give food or drink.
Stay with them while waiting for help.
Every sign above is quoted from the sofidex article on Marijuana intoxication. If you are not sure, err upward — it is always reasonable to be checked.