What It Means When a Biologic Stops Working

When a biologic "stops working", it almost always means one of four different things. Your immune system may have made antibodies that clear or block the drug. The drug may be leaving your body too fast for other reasons, with no antibodies involved. It may be present at good levels while your inflammation has started running through a pathway the drug does not block. Or the drug may be fine and the symptoms are coming from something other than inflammation. (A drug that never worked at all, called primary non-response, is a related but separate story, covered below.) A blood test for the drug level and antibodies, together with a check that inflammation is really there, usually tells your IBD team which of these it is, and each one leads somewhere different. Why the routine bloods matter on these drugs is covered in why you need blood tests on a biologic.

That distinction is the whole point of this article. "It stopped working" sounds like one event, and in patient forums it is often treated as a verdict on you or on the drug. In practice it is a question with several possible answers, and the answer decides whether the next step is adjusting the same medicine, switching to a close relative of it, moving to a different class, or looking somewhere else entirely.

A note on scope before we start. Most of the long-term evidence is on infliximab (Remicade and its biosimilars) and adalimumab (Humira and its biosimilars), the anti-TNF drugs, because they have been used for longest. Newer biologics such as vedolizumab, ustekinumab, risankizumab and guselkumab have far less published data on loss of response and drug-level testing. Where we say we could not find evidence, that reflects our searching of PubMed and Europe PMC, not proof that none exists. Nothing here is advice to change, stop or adjust any medicine; those decisions belong to you and your IBD team together.

The short answer: four problems that look the same from the outside

Each kind of failure feels identical from the sofa: the old symptoms come back. What differs is what is happening in your blood and your bowel, and that is what the tests are for.

The evidence for the middle column comes mainly from an Israeli study of 330 loss-of-response events, which we come back to below (Yanai 2015). The fourth row overlaps with how a flare is confirmed in the first place, which has its own article on telling whether you are in a Crohn's flare, including infection and strictures as look-alikes. We will not rebuild that here.

Primary non-response versus secondary loss of response

There are two clocks, and they mean different things. Primary non-response means the drug never really worked: by the end of the starting (induction) phase, there was no meaningful improvement. Secondary loss of response means it did work, sometimes for years, and then the benefit faded.

The UK PANTS study is the best large dataset on both. It followed 1,610 people with active Crohn's disease starting infliximab or adalimumab for the first time. Primary non-response at week 14 occurred in 295 of 1,241 people who could be assessed, or 23.8%. By week 54, 63.1% of those assessable were not in remission (Kennedy 2019). Two findings from that paper matter for anyone wondering what their own story means:

• The only factor independently linked to primary non-response was a low drug level at week 14. Not age, not smoking, not disease location. That suggests part of what looks like "this drug does not suit me" is actually "not enough of this drug reached the target".
• Carrying on unchanged after primary non-response rarely helped. Only 14 of 113 people (12.4%) who continued standard dosing after not responding went on to remission by week 54.

The study was funded by two UK patient charities and a research charity together with AbbVie, Merck Sharp and Dohme, Napp, Pfizer and Celltrion, companies that make or market the drugs studied. That does not invalidate the findings, but it is worth knowing.

The distinction matters because the next steps differ. Primary non-response with good drug levels suggests the drug's target is not the main driver of your inflammation. Secondary loss of response is more often a story about levels and antibodies, which is often fixable.

Is losing response inevitable?

No, but it is common enough that it is reasonable to expect your treatment plan to change at some point. How common depends heavily on how "loss of response" is defined.

The most-shared figure in Crohn's forums is that "two-thirds lose response by three years", from a thread that drew 78 comments (r/CrohnsDisease thread). It comes from the PANTS three-year follow-up. Among people who had initially responded, the estimated proportion who had lost response was 34.4% at year 1, 54.5% at year 2 and 60.0% at year 3 on infliximab, and 32.1%, 47.2% and 68.4% on adalimumab (Chanchlani 2024). Overall, only around a third of the whole cohort were in remission at three years.

Three details change how those numbers read:

1. "Loss of response" was defined broadly. It counted anyone whose symptoms warranted escalating steroids, immunomodulators or the anti-TNF itself, as well as surgery or leaving the study for treatment failure. Someone whose dose was increased and who then did well for years counts as a loss of response. It is not the same as "the drug was abandoned".
2. The adalimumab year-3 figure is uncertain. Its 95% confidence interval runs from 50.9% to 79.7%, because fewer people remained in follow-up.
3. Not everyone went into the extension. Only 389 of 955 people on infliximab and 209 of 655 on adalimumab entered the two-year extension study, so the later years describe a selected group.

An older review gives a different-looking number. Pooling 16 studies with 2,236 people on infliximab for Crohn's, it found that 37% lost response on average, which worked out at about 13% per patient-year (Gisbert 2009). If 13% a year compounded steadily, about 34% would have lost response by three years, well below PANTS's 60%. We do not think these contradict each other so much as measure different things: Gisbert's review counted the need for dose intensification, PANTS counted any escalation of treatment, and the studies come from different eras of dosing practice. What both agree on is that loss of response is frequent, gradual and not a personal failing.

And the long tail is real. Threads asking whether antibodies are inevitable are full of people on the same drug for eight, twelve or nearly twenty years, alongside people who cycled through four biologics in as many years (r/CrohnsDisease thread). Both experiences are consistent with the data.

What anti-drug antibodies are, and why some matter more than others

Biologics are themselves antibodies, large proteins made in living cells. Your immune system can recognise them as foreign and make antibodies against them. This is called immunogenicity. Anti-drug antibodies can speed up how fast the drug is cleared from your blood, block the part of it that does the work, or both.

Neutralising versus non-neutralising

A neutralising antibody binds the drug in a way that stops it working. A non-neutralising antibody binds elsewhere; it may still speed clearance, but it does not directly block the drug's action. That is why lab reports and drug labels often give two numbers.

How often antibodies appear, drug by drug

These numbers come from different studies with different laboratory methods. Every US label quoted here carries the same warning: differences in assay methods make comparisons between drugs not meaningful. Treat the table as orders of magnitude, not a league table.

The PANTS figures used a "drug-tolerant" assay, which picks up antibodies even when drug is present, so it finds more of them than older methods. The vedolizumab label adds a detail that is easy to miss: among the 20 people with persistent antibodies, 14 had markedly reduced or undetectable drug levels and 15 were not in remission at week 52. So when antibodies to the newer drugs do persist, they can matter; they are just much less common in these trials.

Antibodies are not always permanent

A Belgian study measured infliximab antibodies repeatedly in 90 people with IBD, deliberately enriched with people known to have had antibodies. Of 53 with confirmed antibodies, they disappeared over time in 15 (28%) and persisted in 38 (72%). Only 2 of the 15 with transient antibodies (13%) had to stop infliximab, against 26 of the 38 (68%) whose antibodies persisted (Vande Casteele 2013). We could not find a conflict-of-interest statement for that paper in PubMed, so we cannot say whether there were any. A French cohort found the same pattern: stable antibodies, defined as two consecutive positive results, were linked to loss of response, while transient antibodies were not (Roblin 2015).

This is why a single positive antibody result is often followed by a repeat test rather than an immediate switch. It also explains what people describe in the forums: "I have some antibodies but it's still working" is a real and documented situation, not wishful thinking.

Why drug levels fall even without antibodies

A low level with no antibodies points to the drug being used up or lost faster than it is replaced. Several things are associated with that.

Heavy inflammation can consume and lose drug. In a Dutch study of 30 people with moderate to severe ulcerative colitis starting infliximab, the drug was found in 129 of 195 stool samples (66%), highest in the first days after the first infusion. People who had not responded by week 2 had much higher stool concentrations after day one than responders (median 5.01 versus 0.54 μg/mL) (Brandse 2015). In other words, in severe colitis some of the drug may be leaking out through the ulcerated bowel. That is a small study in severe UC, and how much it applies to Crohn's or milder disease is not known.

Some personal factors were linked to loss of response in PANTS. On infliximab, female sex (hazard ratio 1.47), obesity (1.62), a higher baseline white cell count and the thiopurine dose quartile were each associated with loss of response; on adalimumab, carrying a gene variant called HLA-DQA1*05 was (hazard ratio 1.95) (Chanchlani 2024). The obesity picture is more mixed across other studies, which we go through in the article on being overweight with Crohn's disease. None of these is something you are doing wrong.

Gaps in treatment. Several forum stories involve a missed or delayed dose, an insurance interruption, or a botched infusion, followed by the drug never quite working the same way again (r/UlcerativeColitis thread). The evidence that breaks in therapy raise antibody risk is mostly about infliximab and comes up again below under restarting.

The gene variant people ask about

HLA-DQA1*05 is carried by about 40% of Europeans. In a genome-wide study of 1,240 people with Crohn's starting infliximab or adalimumab, carriers developed antibodies faster (hazard ratio 1.90). The extremes were striking: 92% of carriers on infliximab alone had antibodies at one year, against 10% of non-carriers on adalimumab combined with an immunomodulator (Sazonovs 2020). The authors themselves called for a randomised trial before pre-treatment testing is used routinely.

The picture is not settled. In an analysis of children with Crohn's from a randomised trial, the increase in treatment failure among carriers (hazard ratio 1.58, 95% CI 0.95 to 2.62) and in antibodies (odds ratio 1.96, 0.90 to 4.31) did not reach statistical significance (Adler 2025). So it is a reasonable question to ask your team about, not a test that decides anything on its own.

What drug level and antibody tests actually tell your doctor

This is the test the whole article turns on. A trough level is the amount of drug in your blood just before your next dose, when it is at its lowest. The antibody test is usually run alongside it. Together they sort most loss-of-response episodes into the rows of the table at the top.

The key study is from Israel: 247 people with IBD and 330 suspected loss-of-response events on infliximab or adalimumab (Yanai 2015). It found:

• Above a trough of 3.8 μg/mL for infliximab or 4.5 μg/mL for adalimumab, people were unlikely to respond to either a higher dose or a switch to another anti-TNF. Those cut-offs identified non-responders to those moves with 90% specificity.
• People with high antibody levels had a longer response when switched to another anti-TNF than when their dose was increased.
• People with no or low antibodies did better with a dose increase.
• Among events with confirmed inflammation, people with adequate levels stayed well longer after moving to a different class of drug than after any anti-TNF adjustment.

The study was retrospective, which limits how strongly it can be read, but the logic has held up and is the basis of most testing algorithms.

Does acting on these tests actually help? A Danish randomised trial took 69 people with Crohn's who had lost response to infliximab and assigned them either to a routine dose increase or to treatment chosen by drug and antibody levels. Response at week 12 was similar (58% versus 53%), but costs were 34% lower in the test-guided group (Steenholdt 2014). In other words, the test did not make more people better in that trial, but it avoided giving extra drug to people for whom extra drug was not going to help.

The American Gastroenterological Association guideline suggests testing drug levels when someone on an anti-TNF has active IBD, but it rates this a conditional recommendation based on very low quality evidence, and it made no recommendation on routine testing when you are well (Feuerstein 2017). The guideline's authors declared no conflicts of interest.

Why your number might not match the threshold you read about

If you have looked up your own result, you may have found a confusing spread of "target" numbers. They come from studies asking different questions at different points in treatment, and they genuinely differ.

(μg/mL and mg/L are the same unit.) The induction-phase numbers are higher because drug levels early in treatment behave differently from maintenance levels. A level that is "low" against one row can be fine against another.

There is a second problem that almost no patient-facing page mentions: the same blood sample can give different numbers in different laboratories. A Boston group compared two widely used assay types on the same samples. A commercial laboratory had found and corrected an upward drift in its infliximab and adalimumab results over 2017 to 2019. Even after the correction, the median infliximab result was 9 μg/mL on one method and 5.7 μg/mL on the other, and agreement on whether a sample counted as "therapeutic" was only minimal at the 5, 7 and 10 μg/mL cut-offs. Agreement was better for adalimumab (Papamichael 2021). It was a small study of 45 infliximab and 29 adalimumab samples, funded by Inform Diagnostics.

In the United States, cost is an extra barrier. In a survey of 403 US gastroenterologists, 90.1% used drug-level testing, mostly when someone was losing response, but the top barriers were uncertainty about insurance coverage (77.9%) and high out-of-pocket costs for patients (76.4%) (Grossberg 2018). If testing has not been offered, cost and coverage may be why, and it is fair to ask.

How strong is the evidence that testing helps at all?

Weaker than the confident tone of many clinic leaflets suggests. A 2020 meta-analysis rated every comparison it could make as very low quality. Pooled studies of reactive testing (testing when someone is losing response) versus no testing found failure to reach remission in 57.1% versus 44.7%, a difference that was not statistically significant and points, if anything, the wrong way (Shah 2020). Proactive testing in people who are well looked more promising but rested on few, mostly observational studies.

In the Belgian TAXIT trial, adjusting infliximab to a target range first and then continuing concentration-based dosing was not better than clinically based dosing for remission at one year (69% versus 66%), but it was associated with fewer flares (7% versus 17%) and, after reductions in people with high levels, lower drug costs (Vande Casteele 2015). So testing is clearly useful for understanding why a drug is failing. Whether routine testing improves long-term outcomes is still being worked out.

Before blaming the drug: is it really inflammation?

The first question your team will usually try to answer is not "is the drug failing?" but "is there active inflammation?" Symptoms and inflammation disagree surprisingly often in IBD.

A meta-analysis of 13 studies with 1,703 people found that symptoms meeting the criteria for irritable bowel syndrome were present in about 35% of people with IBD who were thought to be in remission, with odds about four times higher than in people without IBD (Halpin 2012). That means a real share of "my biologic stopped working" is cramping, urgency or loose stools from a sensitised gut, a stricture, bile acid problems or an infection, with the drug still doing its job. Changing biologics will not help those, and it uses up an option.

That is why the usual sequence is: confirm inflammation (blood tests, faecal calprotectin, sometimes imaging or a scope), rule out infection, then look at drug and antibody levels. Your calprotectin result is one piece of this, and the explainer below shows how to read it against your own previous results.

If your symptoms are bothering you but your markers are quiet, the article on ulcerative colitis symptoms while in remission covers what else may be going on, and much of it applies to Crohn's as well.

Does failing one biologic mean the next one is less likely to work?

Somewhat, on average, and the reason the first one failed is the strongest clue.

A meta-analysis of 46 studies looked at a second anti-TNF after the first had failed. In Crohn's, a second anti-TNF after infliximab induced remission in 43% overall. But it varied sharply by why the first was stopped: 61% if it was stopped for side effects, 45% after secondary loss of response and 30% after primary non-response (Gisbert 2015). The evidence in UC was thin: six studies reporting remission gave figures from 0% to 50%.

That pattern fits the four-problem framework. If the first drug failed because of antibodies or side effects, the class may still suit your disease. If it never worked at all, the target may not be what is driving your inflammation, and another drug aimed at the same target has less reason to succeed.

There is one twist. A Danish single-centre study found that people who had made antibodies to infliximab were more likely to make antibodies to adalimumab afterwards (33% versus 0%), and those antibodies were linked to adalimumab failure (Frederiksen 2014). The numbers were small, with 57 people tested on adalimumab, but it is consistent with what many forum users describe: some people seem to make antibodies readily, drug after drug (r/CrohnsDisease thread). Combination with an immunomodulator is one of the strategies teams use for exactly this reason.

The newer drug classes show the same "harder after a failure" pattern. In the ustekinumab trials, the response at week 6 in people who had already failed an anti-TNF was 33.7% to 34.3% versus 21.5% on placebo; in people who had only failed conventional therapy it was 51.7% to 55.5% versus 28.7% (Feagan 2016). Subtracting placebo, the gain was roughly 12 to 13 percentage points after an anti-TNF failure and roughly 23 to 27 points without one. These were two separate trials with different populations, so the comparison is indicative rather than head-to-head. The trials were funded by Janssen, the drug's maker.

Can a biologic that stopped working ever work again?

Sometimes, and it depends on why you stopped it. This question comes up constantly, including from someone who had been through seven biologics and was being advised to return to drugs that had worked years earlier (r/CrohnsDisease thread).

The most-cited figure needs care. A meta-analysis of nine studies found that restarting infliximab achieved remission in 85% at induction and 73% in maintenance, with infusion reactions in 9% (Yang 2021). But those were people who had stopped infliximab while in remission and then relapsed, not people whose infliximab had stopped working. That figure does not apply to someone who lost response.

For the harder case, a French series looked at 61 people with Crohn's who had failed infliximab and then adalimumab, and then went back on infliximab. Remission at weeks 6 to 8 was 42%, and 60% were still on it at 12 months and 51% at 24 months. Of the 29 who eventually stopped again, 13 did so because of intolerance (Gagniere 2015). Restarting was more durable in people who had an immunomodulator alongside both courses and a shorter gap between them. It is a retrospective series from specialist centres, so it shows that re-treatment can work, not how often it would work for you.

Reactions are the main risk. Restarting after a gap, particularly if antibodies were present, can cause infusion reactions, and some forum accounts describe severe ones (r/CrohnsDisease thread). Teams manage this with antibody testing first and precautions around the infusion, which is one more reason this is never a do-it-yourself decision.

Can antibodies be reversed? In a very small Israeli case series, adding an immunomodulator to infliximab in 5 people with antibodies was followed by falling antibody levels, rising drug levels and restored response in all five (Ben-Horin 2013). Five people is far too few to say how often that works, but it shows that antibodies are not always a one-way door.

Can loss of response be prevented?

Partly, and the strategies are your team's to weigh with you, because each carries trade-offs.

Combination therapy. In the SONIC trial of 508 people with Crohn's who had not had immunosuppressants or biologics before, corticosteroid-free remission at week 26 was 56.8% on infliximab plus azathioprine, 44.4% on infliximab alone and 30.0% on azathioprine alone (Colombel 2010). In PANTS, using an immunomodulator alongside the anti-TNF more than halved the rate of developing antibodies (hazard ratio 0.39 for infliximab and 0.44 for adalimumab), and starting it before or on the same day as infliximab worked better than adding it later (Kennedy 2019, Chanchlani 2024). Immunomodulators have side effects of their own, and several people in the forums describe stopping one because of nausea; whether the trade-off is worth it is an individual decision.

Getting the starting phase right. The PANTS authors concluded that low drug levels at the end of induction predicted loss of response by year 3, and suggested higher drug concentrations in the first year might help. They framed this as a hypothesis needing trials, not settled practice.

Not leaving gaps. Forum accounts of drugs never quite working again after an interruption are common, and in the French re-treatment series a shorter gap between courses went with a more durable second course. If insurance, travel or illness threatens a dose, telling your team early gives them a chance to plan around it. If you travel with injectable biologics, flying with Crohn's medication covers storage and security.

What to note down when you suspect your biologic is fading

The most useful thing you can bring is a timeline, not a conclusion. The full method for an IBD diary, including how to log where you are in a dosing cycle, which biosimilar brand you received and the treatment record that follows you between clinics, is in what to track in an IBD symptom diary. For this specific question, the details that matter most are:

• When symptoms returned relative to your doses. Symptoms that bunch up in the days before the next dose are a common early sign people report, and a pattern your team will want to see.
• Any missed, late or changed doses, including a switch to a biosimilar or a change of infusion centre.
• Anything else that changed: a course of antibiotics, a new painkiller, a stomach bug, travel.
• Your previous test results, including the lab used, so new ones can be compared like with like.

If you use Clairop, its one-page report puts your activity score, bowel pattern, medication adherence and lab results together in a single view, which is the shape of information this conversation needs. You can see how that works on the how it works page. A paper log does the same job. If you want help structuring what to ask, the questions to ask about Crohn's disease article has a section for when a drug stops working.

A worked example: two people, same complaint

This is an illustration, not a real case, to show how the same symptom leads to different decisions.

Person A has been on infliximab for three years. Over two months, stools have loosened and they have had some urgency in the week before each infusion. Calprotectin is clearly raised compared with their own earlier results from the same lab. Their trough level is undetectable and antibodies are high. This looks like immunogenic failure. The studies above suggest more of the same drug is unlikely to help, and their team discusses a different drug; whether that is another anti-TNF with an immunomodulator or a different class depends on their history.

Person B describes the same symptoms on the same drug. Calprotectin is normal, the trough level is comfortably within range and there are no antibodies. A stool test rules out infection. Here the drug appears to be working, and the team looks at other explanations: a narrowed section of bowel, bile acid malabsorption or IBS-type symptoms. Switching biologics would have used up an option without addressing the cause.

A third version, Person C, has high calprotectin with a good drug level and no antibodies. That is the mechanistic pattern, and moving to a drug with a different target is the direction the evidence points.

Myths about biologics stopping working

"If it stopped working, I must have done something wrong." Loss of response is common in every large study, and most of the factors linked to it, such as genetics, sex and how severe the inflammation was, are not things anyone controls.

"Antibodies mean the drug is finished." Not always. Some antibodies are transient, and low-level antibodies with a good drug level are interpreted differently from high antibodies with no drug present.

"Everyone ends up making antibodies to everything." Antibody rates vary a great deal by drug. The US labels for the newer IBD biologics report low rates in IBD trials, though label figures cannot be compared directly with each other.

"The 24% Skyrizi antibody rate applies to Crohn's." It is the psoriasis figure. The Crohn's figure in the same label is much lower.

"A level above X means my drug is fine." Thresholds differ by study, by treatment phase and by laboratory method. A good level also does not rule out mechanistic failure; it just tells your team which kind of problem they may be dealing with.

"Once you have failed a drug class, you can never use it again." It depends on why it failed. A second anti-TNF works considerably more often when the first was stopped for side effects than when it never worked.

"A drug that stopped working can never work again." Re-treatment has worked in some people, but the most-quoted success rates come from people who stopped the drug while well, not people who lost response.

When the options feel like they are running out

One of the hardest threads we read was from a young adult with ulcerative colitis, convinced they had thrown away their best treatment by stopping it years earlier and now failing its replacements (r/UlcerativeColitis thread). The replies were kind and practical: second opinions, newer drug classes, and reminders that people routinely find something that works after several failures. Another thread, from someone starting their eighth drug, drew dozens of replies from people in remission on their third, fourth or seventh (r/CrohnsDisease thread).

The number of drug classes for IBD has grown considerably, and a failure on one is information for choosing the next, not the end of the road. For some people surgery becomes part of the plan, and the article on knowing whether you need a colectomy covers how that decision is made in UC. Asking for a referral to a specialist IBD centre or a second opinion is reasonable at any point.

If the weight of this is getting too much, please tell someone. In the US, you can call or text 988 for the Suicide and Crisis Lifeline. In the UK and Ireland, call Samaritans on 116 123. Elsewhere, findahelpline.com lists local services. If you are in immediate danger, use your local emergency number.

The short version

"My biologic stopped working" is a starting point for a few specific questions, not a verdict. Is there real inflammation? Is the drug in my blood at a useful level? Are there antibodies, and are they persistent? The answers separate immunogenic failure, fast clearance, mechanistic failure and symptoms with another cause, and each has a different next step. Loss of response is common, especially with the older anti-TNF drugs, but it is not universal, it is not your fault, and it does not mean you have run out of options. Keep taking your treatment as prescribed, write down what has changed and when, and ask your team what they are checking and why.