Erenumab: what it treats, how it is given, side effects
Last updated September 3, 2026.
Erenumab is a monoclonal antibody - it blocks CGRP, a natural substance in the body that causes migraine headaches. You may know it as Aimovig. A once-monthly injection under the skin, prescribed by the clinician managing your migraines - usually a neurologist or headache specialist after other preventives have fallen short.
What does it treat?
Prevention of migraine headaches in adults.
How is it given?
A prefilled syringe or autoinjector, injected under the skin once a month, around the same day every month - thigh, stomach area, or upper arm, rotating sites. You or a caregiver can inject at home after your doctor demonstrates the technique. The medication comes from the refrigerator: let it sit at room temperature per the instructions before injecting, never heat it, and never shake it. Missed dose: inject as soon as you remember, then set the monthly schedule from that new date - ask your doctor if unsure.
Side effects to know
- Common: injection-site pain, redness, swelling, or itching; constipation - the one to actually watch, because it can escalate; cramps; muscle spasms; mouth sores; and hair loss.
- Serious - call your doctor immediately or get emergency care: the allergic set - rash, hives, itching, swelling of face, throat, tongue, lips, or eyes, trouble swallowing or breathing; constipation with constant stomach pain or tenderness, vomiting, or stomach bloating - that combination is not ordinary constipation; and numb, cold, painful, or discolored fingers or toes.
Who should not take it?
Flag a latex allergy for some device components, constipation problems or bowel motility disorders, and uncontrolled high blood pressure - erenumab can raise it. It is prescribed and followed by the specialist managing your migraines; Pymander does not prescribe injectable biologics, and the drug itself is shipped and stored cold - handle deliveries promptly. If you become pregnant, call your doctor.
When is it an emergency?
Throat or tongue swelling or trouble breathing is a 911 call. Severe stomach pain with vomiting and no stool passage is urgent care. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
What a Pymander AI doctor consult looks like
Illustrative example, not a real member's messages.
Common questions
How is erenumab different from migraine pills?
It is an antibody, not a small-molecule drug: one monthly injection that blocks CGRP steadily, instead of a daily pill. Side effects differ accordingly - no weight gain, no brain fog, no liver-enzyme issues - with constipation and injection-site reactions as the trade. It typically enters after oral preventives have failed or been intolerable, and it is managed by the neurologist or headache specialist, often with specialty-pharmacy shipping and insurance steps.
How do I learn to inject myself?
Your doctor or their nurse demonstrates, and the first injection often happens in the office. The home routine: refrigerator to counter to warm per the instructions (never heated, never shaken), clean the site - thigh, stomach, or upper arm, rotating - inject, dispose in the sharps container. The autoinjector hides the needle entirely if that helps. Nobody is expected to figure it out from the leaflet alone - ask for the hands-on walkthrough.
Why is constipation a big deal on this medication?
Erenumab slows gut motility as a known effect - and the serious version is on the label: constipation with constant stomach pain or tenderness, vomiting, or bloating can signal a bowel obstruction. The management is proactive: fluids, fiber, activity from day one, and a threshold for adding a laxative conversation. The combination above is never waited out - it is a same-day call.
Why does it come cold in the mail?
Antibodies are proteins - heat and freezing degrade them, so it ships cold, lives in the refrigerator (never the freezer), and warms at room temperature before injecting. Handle delivery promptly, do not let it sit on a porch, and if the cold chain clearly failed - warm box, broken gel packs - call the specialty pharmacy before using it. A compromised vial is a replacement, not a gamble.
How long until I know it is working?
Give it three monthly doses: some respond in month one, but the trial pattern is improvement accumulating over the first quarter. The migraine diary is the evidence - count headache days, severity, and rescue-medication use, and bring it to the follow-up. Half as many migraine days by month three is a typical responder; no change by then is a reassessment.
What happens if I miss my monthly injection?
Inject as soon as you remember, then rebuild the monthly schedule from that new date - and check with your doctor if the gap was long. Prevention works on steady blockade; a late month shows up as a rough patch in the diary. Set the reminder a few days ahead so the refrigerator supply and the calendar never fight each other.