Most Aimovig side effects are mild and tend to fade within days to a few weeks after each monthly injection. Because Aimovig is a large antibody molecule rather than a traditional small-molecule drug, it leaves the body slowly, with an estimated half-life of about 28 days. That means it can take roughly three to four months after your last injection for the drug to be mostly cleared from your system, and lingering side effects may persist during that window.
Common Side Effects and Their Timeline
The most frequently reported side effects of Aimovig include injection site reactions (pain, redness, swelling), constipation, and muscle cramps or spasms. Injection site reactions are typically the shortest-lived: soreness or redness at the spot where you injected usually resolves within a few days, similar to what you’d experience after a flu shot.
Constipation is the side effect that generates the most concern. The FDA’s prescribing information notes that in a majority of reported cases, constipation appeared after the very first dose, though some people develop it later in treatment. Data from a five-year open-label study published in Cephalalgia found that constipation tends to dissipate over time with continued use, meaning your body often adjusts after the first few monthly doses. For most people, constipation improves within the first one to two weeks of each injection cycle, peaking in the days right after the shot and easing as the month goes on.
Muscle cramps follow a similar pattern. They’re generally mild, come on in the first week or two after injection, and resolve before the next dose is due.
Why Side Effects Linger After Stopping
Aimovig works by blocking a receptor involved in pain signaling (the CGRP receptor). Unlike a pill that’s out of your bloodstream in hours, Aimovig is a monoclonal antibody that the body breaks down slowly through natural protein recycling. After a single 140 mg injection, blood levels peak around 4 to 11 days and then decline gradually over weeks.
The drug has two elimination pathways. At lower concentrations, it’s cleared mainly by binding to its target receptors, which is a slower, saturable process. At higher concentrations, the body breaks it down through a more general protein degradation pathway. The practical result is that after you stop injecting, meaningful levels of the drug remain in your system for about three months. If you experienced side effects while on Aimovig, they may take that long to fully resolve after your last dose.
Constipation That Becomes Serious
In rare cases, Aimovig-related constipation goes beyond simple discomfort. The FDA added a warning about constipation with serious complications, including cases that required hospitalization. This is uncommon, but it’s worth knowing the signs: if you go more than several days without a bowel movement, develop significant abdominal pain or bloating, or notice symptoms getting worse rather than better with each injection cycle, that warrants a conversation with your prescriber. Some people manage mild constipation successfully with increased fiber, fluids, and over-the-counter options. Others find it persistent enough to reconsider the medication.
Blood Pressure Changes
Post-marketing reports have flagged blood pressure elevations in some Aimovig users. This was not a prominent finding in the original clinical trials but emerged after wider use. The timeline for blood pressure changes isn’t as well-defined as for constipation, and it can occur at any point during treatment. If you’re monitoring your blood pressure at home and notice a new upward trend after starting Aimovig, that information is useful to bring to your next appointment. Blood pressure typically normalizes after the drug clears your system, though how quickly depends on your individual health factors.
What the Five-Year Data Shows
Long-term safety data is reassuring for most users. A five-year open-label extension study found no new safety signals emerging with prolonged use. The side effect profile remained consistent with what was seen in shorter trials, and notably, constipation was less of an issue in the long-term data than in the initial placebo-controlled studies. This supports the pattern that the body adapts to the drug over time, and early side effects are the most likely to bother you.
No evidence of cumulative toxicity or worsening side effects over years of use was found, which is meaningful for people planning to stay on Aimovig long-term for migraine prevention.
What to Expect If You Stop
If you stop Aimovig because of side effects, the general timeline looks like this: side effects that track with each injection cycle (constipation peaking in the first week, muscle cramps) will not recur after the last dose wears off. Most people notice improvement within four to six weeks of their last injection, with full resolution by about three months as the remaining drug is cleared. There’s no formal “washout period” published in the prescribing information, but many headache specialists use the three-to-four-month estimate when planning transitions to a different preventive treatment or advising on pregnancy planning.
If your side effects don’t improve within that window, they may not be related to Aimovig at all, and it’s worth exploring other causes with your provider.