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
Seek emergency help now for:
Chest pain, severe shortness of breath, or collapse
A very fast or clearly irregular heartbeat with weakness or dizziness
A seizure, loss of consciousness, or difficulty waking
Severe confusion, agitation, or unusual behaviour
High temperature with marked restlessness, vomiting, or a racing heart
Any suspected overdose in someone who cannot be safely observed
If the medicine was taken intentionally, call emergency services or a poison centre now.
Stay with the person if it is safe to do so and remove access to remaining medicines.
In the United States, you can also call or text 988 for crisis support, but emergency symptoms still require emergency medical care.
Routine follow-up is appropriate if you have gradually developed palpitations, tremor, sweating, sleep problems, or unexplained weight loss while taking thyroid medicine but have no emergency symptoms.
And for anyone, someone who:
is unconscious, or cannot be woken
you believe has taken an overdose or swallowed something poisonous
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 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
2
Is any of this happening?
Be seen today
Contact a poison information service promptly after a suspected overdose, even if there are no symptoms.
Have the medicine container, tablet strength, estimated number taken, and time of ingestion available.
Do not delay the call while trying to calculate an exact amount.
3
Does any of this apply?
Book an appointment
Arrange a medication review and thyroid blood tests rather than changing the dose yourself.
And for anyone, someone who:
is having side effects from a medicine, or is struggling to take it as prescribed
Every sign above is quoted from the sofidex article on Thyroid preparation overdose. If you are not sure, err upward — it is always reasonable to be checked.