Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Contact emergency services or a poison centre immediately if too much nitroglycerin may have been swallowed, sprayed, applied, or given.
Do this even if the person currently feels well.
Call emergency services at once for:
Elsewhere, use the local poison centre or emergency number.
And for anyone, someone who:
It does not replace urgent care for new symptoms.
Routine follow-up is appropriate after recovery to review medicine use, storage, interactions, and the condition for which nitroglycerin was prescribed.
And for anyone, someone who:
The article also says
Do not make the person vomit.
Do not give food, drink, or home remedies unless a poison specialist advises it.
Do not let a dizzy or faint person stand or walk, and do not have them drive.
If it can be done safely, remove any nitroglycerin patch while waiting for help.
Keep the package, applicator, or remaining medicine so responders can identify the product.
In the United States, Poison Help can be reached at 1-800-222-1222.
Every sign above is quoted from the sofidex article on Nitroglycerin overdose. If you are not sure, err upward — it is always reasonable to be checked.