Picture a lift that has stopped between floors. The doors are shut, the little display has gone blank, and nobody has told you whether the wait will be thirty seconds or thirty minutes. You are not in danger. You are simply not knowing, and your body has decided that this is an emergency anyway. Your shoulders are up around your ears, you have pressed the button three times, and you are already running through every version of how this ends.
Now think of where else you have stood in that lift. It might be the waiting list for an ADHD assessment, when you have been told the appointment will come but not when. It might be a diagnosis that is only a few weeks old, with a great deal still unexplained. It might be a letter from school, read three times at the kitchen table, that says a meeting is needed and not what for. It is half past eleven on a bad night, and the question that keeps you awake is never the answer. It is the gap before it.
Psychologists have a name for how hard that gap can feel: intolerance of uncertainty, often shortened to IU. It is one of the most useful ideas in modern mental health research, and it explains something you may have wondered about for years. This post looks at what the research says, what it does not say, and what you can try tonight.
What intolerance of uncertainty actually means
The concept grew out of work on chronic worry by researchers including Michel Dugas at Concordia University in Canada, and it was developed further by Nicholas Carleton at the University of Regina. Put plainly, intolerance of uncertainty is a tendency to experience not knowing as threatening in itself.
That is different from disliking surprises, which is simply a matter of taste. IU is closer to a conviction, held somewhere below conscious thought, that if you cannot predict what is coming then you cannot be safe. And if you cannot be safe, the sensible thing to do is find out, check, prepare, rehearse or avoid, until the doubt goes away.
The trouble is that the doubt rarely goes away. Uncertainty is the ordinary condition of being alive, so a mind that treats it as an emergency will find emergencies everywhere: in a delayed text, an unexplained ache, a results letter that has not yet arrived, a friend who has gone quiet. Each one is a small unknown, and each one asks you to do something about it.
Have you ever noticed that it is not the bad news that undoes you, but the hour before the news arrives? If so, you have already met this idea, even if nobody gave it a name.
Why researchers keep coming back to it
IU was first tied to generalised anxiety disorder, the diagnosis in which worry becomes constant and hard to control. But it has not stayed in one place. A recent study published in Epidemiology and Psychiatric Sciences followed adolescents across three waves over twelve months, and found that intolerance of uncertainty predicted later symptoms of both generalised anxiety and depression.
If you are a teenager, or you are raising one, that finding is worth a moment. A young person who was less able to bear not knowing was more likely, a year on, to be more anxious and more low. That does not prove IU causes those difficulties, and one study of adolescents cannot be stretched to cover every adult. But it fits a picture in which IU is not only a symptom of feeling bad. It looks like a habit of mind that helps to feed it.
And a habit, unlike a fixed trait, can be changed.
How not knowing turns into worry
It helps to see how the machinery runs, because once you can see it, you can start to interrupt it. Most accounts describe a loop with four parts.
The trigger
Something ambiguous appears: no reply, an odd sensation, an email that says only “can we talk?” The ambiguity itself is the trigger, not any actual danger.
The catastrophic reading
Where a relaxed mind would shrug and say “I’ll find out,” your mind fills the gap with the worst available answer. That is not pessimism for its own sake. It is an attempt to be ready.
The safety behaviours
Next come the things you do to get rid of the doubt. You ask your partner for the fifth time whether it will be all right. You refresh the inbox, the tracking page, the results portal. You over-prepare, put off a decision in case it is the wrong one, or avoid the situation altogether. Psychologists call these safety behaviours: actions that lower anxiety in the short term.
The relief that teaches the wrong lesson
Here is the cruel part. Each safety behaviour works, for a few minutes. The anxiety drops, and your brain files away a conclusion: that was dangerous, and checking is what saved me. So the next unknown feels a little more threatening, and the next urge to check a little stronger.
The very thing that soothes you is teaching you that you cannot cope without it.
This is why being told to “just stop worrying” never works. It asks you to switch off a system that believes it is protecting you.
What treatment does about it
The encouraging news is that intolerance of uncertainty can be reduced, and the research on how is now substantial.
In 2023, Miller and McGuire published a meta-analysis in the Journal of Affective Disorders on what treatments do to IU. A meta-analysis pools the results of many separate studies into one overall estimate, which makes it sturdier than any single trial. As summarised in a later review, they found that behavioural approaches reduced IU with a medium effect size (Hedges’ g of 0.54), while cognitive approaches and mindfulness-based approaches produced larger reductions (0.95 and 0.98 respectively). For orientation, an effect size around 0.5 is usually described as medium, and anything approaching 0.8 as large. All three of those figures are at least medium, and two are well beyond it.
Their analysis also pointed to who tended to gain most. The effects were larger for people with both anxiety and depression, in longer treatment protocols, and in individual therapy rather than group therapy. If you are weighing up what kind of help to ask for, that last point is one to raise with a clinician, not one to act on alone.
Two other pieces of work add to the picture. Wilson and colleagues reported in 2023 that CBT aimed specifically at intolerance of uncertainty was more effective for generalised anxiety disorder than traditional CBT. (CBT, or cognitive behavioural therapy, is a structured talking therapy that works on the links between your thoughts, feelings and behaviour.) And in 2024, Näsling and colleagues published a systematic review in Clinical Psychology & Psychotherapy that looked across the studies at how psychotherapy affects IU.
The pattern is consistent. Something that looks like a permanent feature of your personality turns out to respond to being worked on directly.
What this research cannot promise you
Here I want to slow down, because hope without honesty helps no one. These limits are not a reason to give up on the findings. They are there to protect you from expecting too much, and from blaming yourself if things move more slowly than a headline number suggests.
Most studies in this field compare treatment with a waiting list, not with another active therapy. That tells you a treatment beats doing nothing. It does not tell you it beats the next best option.
The evidence is also thinner for neurodivergent and developmental groups. If you have ADHD, or autism, or you are the parent of a child who does, uncertainty may land differently for you, and this research does not yet tell us how. Anything said about you from here is an extension of the findings, not a result of them. So treat what follows as a reasonable experiment, not a proven prescription, and judge it by how it works for you.
Nor is any of this a claim that uncertainty is a personal failing. If your income is unstable, your housing is insecure or you are waiting months for an appointment, your alarm is answering something real. The point is not that you should feel calm about a genuinely uncertain situation. The point is that the size of your reaction is something you can work on, even while the situation stays exactly where it is.
If worry is taking up hours of your day, keeping you from sleep or narrowing what you are willing to do, please speak to your GP. In the UK you can also refer yourself directly to NHS Talking Therapies without seeing your GP first. If you are on a waiting list for that first appointment, the steps below are gentle enough to begin with in the meantime.
Six ways to practise not knowing
None of these will make uncertainty pleasant. They are designed to teach your mind, through repetition, that not knowing is survivable. Pick one. You do not need all six.
- Name it precisely. When the tightness arrives, say to yourself, “This is intolerance of uncertainty, not a prediction.” Naming the process separates the feeling from the forecast, and it is quick enough to do in a corridor or a queue.
- Ask what the safety behaviour is for. Before you check, reassure or rehearse, pause and ask what you are hoping it will buy you. Often the honest answer is “certainty that does not exist.”
- Run a behavioural experiment. Choose a small, low-stakes unknown, such as leaving a message unanswered for an hour or booking a restaurant you have not researched. Write down what you predict will happen, then record what did. Over a few weeks, you build your own evidence about whether your forecasts are as reliable as they feel.
- Delay before you check. Postpone the urge by ten minutes, then twenty. You are not forbidding yourself. You are watching the urge rise and fall, which teaches it that it does not have to be obeyed.
- Separate solvable from unsolvable worries. If there is something you can do today, such as ringing the school office or writing your questions for the assessment, do that. If there is not, write “nothing to do yet” on the page and leave it there.
- Build in a little planned uncertainty. Walk a different route home. Order the dish you cannot picture. Each is a small vote for the idea that surprises can be survived.
The first few attempts often feel awkward. The urge may not shrink at all. What tends to shift first is smaller: a few minutes longer before you check, or the moment you notice yourself reaching for the phone and reach anyway, but with your eyes open. That moment counts.
The quieter reward
Learning to bear uncertainty does not make you careless. You will still plan, still check the important things once, still prepare where preparation helps. What changes is that the plan stops being a hiding place.
Some nights this will feel impossible. It will not work. That is allowed, and you can try again tomorrow.
It is worth picturing what a good week of this might look like, because it is rarely dramatic. You still open the letter. You still ask the question at the appointment. But on the Wednesday when the email does not arrive, you make a cup of tea and go back to what you were doing for another hour, and you notice afterwards that you did. Nobody else would have seen it happen. You would know.
Tonight, when the screen lights up with a name you were not expecting, or the letter is still on the table, try one small thing. Let it wait. Notice the endings your mind starts to write, and notice that none of them has happened. That gap between the ring and the answer is exactly where this skill is built, and every time you stay in it a little longer, you show yourself that you are more capable than the worry has been telling you.
Source: Miller & McGuire (2023), meta-analysis of treatment effects on intolerance of uncertainty, Journal of Affective Disorders, with effect sizes as reported in a later review; Wilson et al. (2023), IU-targeted CBT compared with traditional CBT for generalised anxiety disorder; Näsling et al. (2024), systematic review of the effects of psychotherapy on intolerance of uncertainty, Clinical Psychology & Psychotherapy; three-wave, 12-month study of intolerance of uncertainty as a prospective predictor of generalised anxiety and depression in adolescents, Epidemiology and Psychiatric Sciences (2026).
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