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 now if someone:
Has a seizure, collapses, or cannot be woken
Has severe confusion or rapidly worsening coordination
Has trouble breathing
Has taken a large or unknown amount of lithium
Has intentionally taken extra lithium or may be at risk of self-harm
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
Get urgent medical advice if you take lithium and develop new vomiting, diarrhoea, worsening tremor, unusual drowsiness, weakness, slurred speech, confusion, or unsteady walking.
Do not wait for a routine blood test to decide whether symptoms matter.
3
Does any of this apply?
Book an appointment
For routine follow-up, arrange a review if you notice a persistent change in thirst, urination, tremor, or medication side effects without signs of acute toxicity.
Regular reviews are also appropriate after changes to kidney health or other medicines.
The article also says
Do not make the person vomit.
Take the medicine packet or container to the hospital if it is safe to do so.
Every sign above is quoted from the sofidex article on Lithium toxicity. If you are not sure, err upward — it is always reasonable to be checked.