Call your local emergency number now (911 in the US and Canada, 112 in the EU, 999 in the UK, 000 in Australia) if you see any of the signs in the first five sections below. Do not drive yourself. Do not wait to see whether it passes.
1. Severe allergic reaction (anaphylaxis)
It usually starts within seconds or minutes of an injection and can get worse fast [1].
- Trouble breathing, wheezing, or noisy, high-pitched breathing
- Swelling of the face, eyes, lips or tongue; trouble swallowing; a hoarse or whispering voice
- Hives, widespread itching or flushing together with any other sign on this list
- Chest tightness, a racing or pounding heartbeat
- Dizziness, feeling faint, collapse
- Sudden belly pain, vomiting or diarrhoea straight after an injection
What to do [1]:
- Call emergency services.
- If the person has an adrenaline (epinephrine) auto-injector or nasal spray, use it straight away.
- Lay them flat and raise their feet, unless they are vomiting or struggling to breathe in that position.
- Give nothing by mouth if they have trouble breathing.
- Go to hospital even if the symptoms ease. Reactions can return.
2. Chest pain or signs of a heart attack
- Pain, pressure or discomfort in the centre or left side of the chest
- Pain in the jaw, neck, back, or one or both arms or shoulders
- Shortness of breath
- Feeling weak, light-headed or faint; a cold sweat
- Unusual tiredness, nausea or vomiting can be the main signs, more often in women
Call emergency services immediately. Faster treatment means less damage to the heart [2].
3. Severe abdominal pain
- Severe pain in the upper belly that does not go away, with or without vomiting, sometimes spreading through to the back. On GLP-1-type drugs this is the labelled warning sign of pancreatitis: stop the drug and get urgent care [3][4].
- Severe pain under the right ribs, especially with fever, or yellowing of the skin or eyes (possible gallbladder disease) [3][4].
- Vomiting or diarrhoea that will not stop, so that you cannot keep fluids down. Dehydration on these drugs can injure the kidneys [3][4].
4. Fainting, collapse, confusion or signs of stroke
- Fainting or nearly fainting, especially soon after an injection
- New confusion, slurred speech, a seizure, or a person who cannot be woken
- Sudden loss of vision in one or both eyes, sudden weakness or numbness of the face, arm or leg, trouble speaking, or a sudden severe headache (possible stroke)
- A very fast, very slow or irregular heartbeat with dizziness
- In someone who also uses insulin or other diabetes medicine: shaking, sweating and confusion can mean dangerously low blood sugar [3][4]
5. Infection that is spreading
Most injection-site redness is minor. These signs are not [5][6][7]:
- Redness, warmth or swelling that is spreading quickly, or red streaks running from the injection site
- Fever, chills, or shivering together with a red, hot, painful injection site
- Skin that blisters, turns dark, or hurts far more than it looks like it should
- Any sign of sepsis: confusion or disorientation, shortness of breath, a high heart rate or weak pulse, extreme pain, clammy or sweaty skin. Sepsis is a life-threatening emergency [6].
6. Urgent, but not always an ambulance
Get medical help the same day (urgent care, an out-of-hours service, or an emergency department):
- You injected the wrong amount or cannot work out how much you injected. In the US, Poison Help answers 24 hours a day on 1-800-222-1222 [9]. Elsewhere, call your national poison centre or medical advice line. Have the vial in front of you.
- An erection that lasts four hours or more (reported with melanocortin drugs). This is an emergency department problem: delay risks permanent damage [8].
- A hot, hard, painful lump at an injection site, with or without pus.
- New blurred vision that comes on gradually.
- Someone else was stuck by your used needle. Wash the area with soap and water and seek medical advice straight away. [10]
What to tell responders
- The name of the substance, the amount, the time, and where on the body it was injected
- Everything else taken that day, including prescription medicines, alcohol and supplements
- Bring the vial, pen or packaging with you
Say exactly what was used. Medical staff are there to treat you, and an accurate answer saves time.
Sources
Checked 13 November 2026.
- MedlinePlus Medical Encyclopedia (U.S. National Library of Medicine). "Anaphylaxis." https://medlineplus.gov/ency/article/000844.htm
- U.S. Centers for Disease Control and Prevention. "About Heart Attack Symptoms, Risk, and Recovery." https://www.cdc.gov/heart-disease/about/heart-attack.html
- Tirzepatide injection (Zepbound), US prescribing information, DailyMed. https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=487cd7e7-434c-4925-99fa-aa80b1cc776b&type=display
- Semaglutide (Wegovy), US prescribing information, DailyMed. https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=ee06186f-2aa3-4990-a760-757579d8f77b
- U.S. Centers for Disease Control and Prevention. "About Cellulitis." https://www.cdc.gov/group-a-strep/about/cellulitis.html
- U.S. Centers for Disease Control and Prevention. "About Sepsis." https://www.cdc.gov/sepsis/about/index.html
- MedlinePlus Medical Encyclopedia. "Subcutaneous (SQ) injections." https://medlineplus.gov/ency/patientinstructions/000430.htm
- American Urological Association / Sexual Medicine Society of North America. "Diagnosis and Management of Priapism: AUA/SMSNA Guideline (2022)." https://www.auanet.org/guidelines-and-quality/guidelines/diagnosis-and-management-of-priapism-aua/smsna-guideline-(2022
- U.S. Health Resources and Services Administration. "Poison Help" (national poison centre line, 1-800-222-1222). https://poisonhelp.hrsa.gov/
- U.S. Food and Drug Administration. "Safely Using Sharps (Needles and Syringes) at Home, at Work and on Travel." https://www.fda.gov/medical-devices/consumer-products/safely-using-sharps-needles-and-syringes-home-work-and-travel