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 a possible drug reaction causes:
Difficulty breathing, wheezing, or throat tightness
Swelling of the tongue or throat
Faintness, confusion, collapse, or pale and clammy skin
A rapidly worsening reaction affecting breathing or circulation
Painful blistering or peeling skin, especially with mouth or eye sores
Use an adrenaline auto-injector immediately if prescribed and the symptoms match your emergency plan.
Call emergency services afterward, even if you begin to feel better.
And for anyone, someone who:
is struggling to breathe, gasping, choking, or cannot get words out
you believe has taken an overdose or swallowed something poisonous
Other emergency signs, for anyone
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
2
Is any of this happening?
Be seen today
Seek urgent medical assessment for a widespread rash with fever, facial swelling, swollen glands, mouth sores, skin pain, or signs of organ problems such as yellow skin, dark urine, reduced urination, chest pain, or unusual breathlessness.
Contact a healthcare professional promptly about a new rash, hives, or swelling after starting a medicine, even if you otherwise feel well.
3
Does any of this apply?
Book an appointment
Routine follow-up is appropriate for an old or uncertain allergy label when you have no current symptoms, especially if it limits useful treatment.
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 Drug allergies. If you are not sure, err upward — it is always reasonable to be checked.