Willpower and ego depletion: does self-control really run out, and what helps instead?

You resolve to study, but after work you just cannot make yourself start; or you hold back all day, then raid the fridge at night and wonder whether you simply have a weak will. A famous theory explains experiences like these: “ego depletion”. The idea is that self-control draws on a limited resource, so after you have held back once, less of it is left and your self-control slips on the next task (Baumeister et al., 1998). It is also widely known through the metaphor of willpower as a muscle that tires with use (Muraven & Baumeister, 2000). This guide sets out how research has supported this idea, and how it has been shaken.

The short answer is that the effect of “willpower running out after you hold back once” turned out much smaller than expected, or barely visible, in large replication studies. In a preregistered replication in which 23 laboratories ran the same procedure with 2,141 people, the effect was small, d = 0.04, and its 95% confidence interval (−0.07 to 0.15) included zero (Hagger et al., 2016). A 2021 project with 36 laboratories and 3,531 people, led by Kathleen Vohs, a long-time ego-depletion researcher, found no effect in its planned analyses, and the authors concluded that any effect is likely to be small (possibly zero) (Vohs et al., 2021). The claim that self-control runs on glucose in the blood also had weak evidence behind it (Vadillo et al., 2016).

That does not mean self-control is meaningless. People who had more self-control as children had, on average, better health, finances and criminal records at 32. Studies like this show links, though, not proven causes (Moffitt et al., 2011). Interestingly, people with more self-control reported fewer efforts to resist temptation, and relied more on good habits (Hofmann et al., 2012; Galla & Duckworth, 2015). So rather than “how to build up your powers of restraint”, this guide focuses on setting up situations and habits so that you need to hold back less.

The guide covers ego-depletion theory and the glucose hypothesis, the results of large replications and what each side argues, the effect of beliefs about willpower, what self-control is really linked to, and realistic methods in light of the research. How habits take hold is covered in the habits guide, putting things off in the procrastination guide, and trouble focusing in the concentration guide. mind.io does not offer a test that measures willpower or self-control.

Ego-depletion research began with experiments by the US psychologist Roy Baumeister’s team in 1998. In the first, people who had to eat radishes instead of tempting chocolates gave up sooner on unsolvable puzzles than people who had not had to use self-control over eating. Making a meaningful personal choice reduced persistence in a similar way, and suppressing emotions lowered performance on solvable word puzzles afterwards. The team read this as a sign that these seemingly unrelated acts share one common resource, and that the resource is limited (from the abstract; Baumeister et al., 1998).

The idea was summed up in the metaphor of willpower as a muscle. Exerting self-control uses up its strength, making the next act of self-control more likely to fail, and coping with stress, managing a bad mood and resisting temptation all draw on that same strength (Muraven & Baumeister, 2000). Hundreds of experiments tested the idea (Carter et al., 2015), and a 2010 meta-analysis of 83 studies reported a medium-sized effect (d = 0.62). In that analysis, people who had done a depleting task also reported more effort, more difficulty and more fatigue (Hagger et al., 2010; Carter & McCullough, 2014).

In 2007 came the claim that this “strength” was blood glucose. A paper with nine studies reported that self-control tasks lowered blood glucose, that lower glucose after a first task predicted poorer performance on the next, and that a glucose drink removed the impairment. Its subtitle was “Willpower is more than a metaphor” (from the abstract; Gailliot et al., 2007; Vadillo et al., 2016).

Objections soon followed. One critic argued that, in light of neurophysiology, the premise that a self-control task lowers glucose more than other tasks do is unlikely to be true (from the abstract; Kurzban, 2010), and in four experiments, blood glucose measured precisely under standardised conditions was not used up any faster by self-control. Instead, merely rinsing the mouth with a carbohydrate solution, without swallowing it, improved self-control straight away, while blood glucose did not rise. The authors suggested that carbohydrates may act on motivation rather than as fuel (from the abstract; Molden et al., 2012). A 2016 statistical re-examination of the glucose studies found signs of publication or reporting bias and weak evidential value, and advised against drawing any conclusion about glucose’s role in self-control (Vadillo et al., 2016).

Then came studies that re-examined the size of the effect. Applying methods that correct for small-study bias to the data of the 2010 meta-analysis revealed strong signs of publication bias, and suggested the effect might be no different from zero (Carter & McCullough, 2014). A 2015 meta-analysis that also gathered unpublished studies concluded that there is very little evidence that ego depletion is real, at least when measured with the methods most often used in the laboratory (from the abstract; Carter et al., 2015). On the other side, it was argued that the correction method had been used inappropriately, and that the effect may depend on which task is used to deplete people (from the abstract; Dang, 2018).

The turning point was a preregistered replication in 2016, in which 23 laboratories followed the same procedure, published in advance, with 2,141 people; the procedure was reviewed by Baumeister, who first proposed the theory. People did a task of pressing a button when a word on the screen contained an “e”: one group did it as is, the other followed the rule “do not press if the ‘e’ is next to a vowel or one letter away from one”. Their performance on a task that required holding back responses was then compared. The effect was small, d = 0.04, and its 95% confidence interval (−0.07 to 0.15) included zero (Hagger et al., 2016). All but one of the participating laboratories had predicted a meaningful effect in advance (Hagger & Chatzisarantis, 2016).

Baumeister, who proposed the theory, and fellow researcher Vohs objected. They argued that the depleting version of the task lacked an initial habit-forming phase, so there was “nothing to override”, and that it may not have depleted people enough. The replication’s organisers replied that, under time pressure, participants still had to hold back the urge to press for every “e”, so the task did demand self-control (Hagger & Chatzisarantis, 2016).

Two more large studies followed. In one, with 12 laboratories and 1,775 people, a colour-naming task (the Stroop task) was followed by a task requiring people to look away from a target, and a small but significant effect appeared (d = 0.10) (from the abstract; Dang et al., 2021). A 2021 project with 36 laboratories and 3,531 people, led by Kathleen Vohs, a long-time ego-depletion researcher, used two procedures chosen as typical of the field. In the planned analyses the effect was not significant (d = 0.06), and the data were 4 times more likely under the hypothesis of no effect than under the hypothesis of an effect. Only an exploratory analysis of everyone, ignoring the exclusion rules, found a very small significant effect (d = 0.08) (Vohs et al., 2021).

These authors concluded that ego depletion is not as reliable or robust as previously assumed, and that the effect is likely small (possibly zero). An exploratory result did suggest a larger effect in people who felt more tired after the first task, and they added that readers sceptical of the theory and readers sympathetic to it may read the findings differently (Vohs et al., 2021). Feeling drained after effort is real, but some argue there is no need to read it as “running out of fuel”: instead, the priority given to what you “have to” do and what you “want to” do shifts (from the abstract; Inzlicht et al., 2014). These studies have not proven that ego depletion does not exist at all, but the claim that holding back once, briefly, drains your willpower rests on weaker evidence than it seemed.

One of the best-known twists in ego-depletion research concerned beliefs. A 2010 study involving Carol Dweck, known for research on growth mindset, reported that only people who believed willpower to be a limited resource showed lower self-control after a depleting task, while those who believed it was not limited did not. Studies that changed people’s beliefs experimentally found the same, and a field study that followed people over time found that, in demanding periods, beliefs about willpower predicted changes in eating, procrastination and effort towards goals (from the abstract; Job et al., 2010). Mindset research in general is covered in the growth mindset guide.

In another study that followed students, the same team reported that students who believed willpower is not limited managed their time better, procrastinated less, and ate less unhealthy food and made fewer impulse purchases when they faced heavy demands, and that among students with a heavy course load they also earned higher grades (from the abstract; Job et al., 2015). A study of 1,177 Japanese university students likewise found that the belief that willpower is limited went with lower grades only among students taking heavy course loads (from the abstract; Sakurai & Watanabe, 2019).

The laboratory result, however, was not confirmed when it was tested again. A preregistered 2023 replication of the first experiment of the 2010 study (60 people), with a larger sample (187 people), found neither an ego-depletion effect nor a difference by belief. The replication team said that, together with other failed replications, this casts doubt on the original claim, while acknowledging that their own study may not have been large enough to detect the effect. Veronika Job, who led the original research, suggested that the blurred text shown in the depletion condition of the original experiment, which the replication did not use, may have made the difference (Carruth et al., 2023). In the 2021 study with 3,531 people, beliefs about willpower did not change the size of the effect either (Vohs et al., 2021).

In sum, there are studies in which seeing willpower as plentiful goes with better everyday self-regulation and grades, but most of them look at links, so they cannot show that the belief is the cause. The experimental finding that a belief alone switches ego depletion on and off was not confirmed in preregistered replications. Telling yourself that “willpower is unlimited” is unlikely to be enough on its own, and the research described below points towards changing situations and habits instead.

Ego depletion being shaken does not make individual differences in self-control disappear. The best-known study followed 1,037 children born in one year in Dunedin, New Zealand, to the age of 32 (96% stayed in the study). The researchers measured self-control at ages 3 to 11 by combining ratings from observers, teachers, parents and the children themselves. The lower people’s self-control as children, the more health problems, substance dependence, money problems and criminal convictions they had at 32, and the links remained after accounting for intelligence and the social class of the family they grew up in. Comparing the fifth with the most self-control and the fifth with the least, 11% against 27% had several health problems, and 13% against 43% had a criminal conviction (Moffitt et al., 2011).

The same paper compared 509 pairs of British twins (non-identical, same-sex pairs) and reported that, even when growing up in the same family, the twin with less self-control at age 5 was more likely to have started smoking at 12. As the researchers stated, though, this was an observational study. Self-control in childhood and in young adulthood were only moderately related (r = 0.30), and those whose self-control improved in between had better outcomes at 32. The researchers added that it is unclear whether change that happens naturally is the same as change brought about by an intervention (Moffitt et al., 2011).

A meta-analysis of 102 studies (32,648 people) on self-control questionnaire scores and behaviour also found small to medium links. Their size varied greatly from one area of life to another, and self-control was more strongly linked to automatic behaviours than to behaviours that take conscious effort (from the abstract; de Ridder et al., 2012). Self-control is an umbrella term that spans concepts used across disciplines, such as conscientiousness (Moffitt et al., 2011). If you want to see five personality traits, conscientiousness among them, as scores, you can take the Big Five test, but it does not measure willpower.

The “marshmallow test” often comes up when childhood self-control is discussed. The original finding, that how long children waited before eating a treat was strongly linked to their achievement as teenagers (SAT scores, for example), came from small, highly selective samples (35 to 89 children) from the Stanford University community. A 2018 replication that followed 918 more varied US children (focusing on 552 whose mothers had not finished college) found that waiting one minute longer at age 4 was linked to achievement at 15, but the link was half the size reported in the original studies, and it shrank by two thirds after accounting for family background, early cognitive ability and the home environment. Links with behaviour problems at 15 were much smaller and rarely significant (Watts et al., 2018). A child’s ability to wait, on its own, cannot predict their future.

Are people with more self-control simply better at resisting temptation? In a study in which 205 adults recorded their desires whenever a beeper went off over a week (7,827 reports), people with more self-control reported fewer attempts to resist temptation, not more (Hofmann et al., 2012; Galla & Duckworth, 2015). In a study that tracked people’s temptations and goals over a semester, too, what made the difference to reaching goals was not how hard people resisted temptations but how often they met them. Merely experiencing temptations made people feel more depleted, and effortful self-control was unrelated to goal attainment in every analysis (from the abstract; Milyavskaya & Inzlicht, 2017).

A paper combining six studies (2,274 people) reported that people with more self-control had more good habits, such as healthy snacking, exercise, regular sleep and studying, and that these habits linked self-control with good outcomes. The authors suggested that good habits may matter more as a link than effortful inhibition, but stated that, as the studies were not experiments, cause and effect cannot be confirmed (Galla & Duckworth, 2015). How habits take hold is covered in the habits guide.

Self-control researchers explain results like these with “situational strategies”: choosing or changing the situation before temptation grows, such as sitting far from where drinks are poured at a party, asking the waiter not to bring the dessert trolley, or going to the library without a phone. Because impulses grow stronger over time, acting early may work better, and because it involves less of a struggle, it may not even be recognised as self-control (Duckworth et al., 2016a).

There is an experiment that tested this directly, in which 159 US university students were split into three groups and set a study goal for the week: one group changed their surroundings to put temptations out of sight, another used the strategy of holding back when temptation came, and the third did nothing in particular. A week later, the group that changed their surroundings said they had met their goals better and felt less tempted. These were self-reports from one university’s students, though, and the authors named the possibility that students answered as expected as a limitation (Duckworth et al., 2016b).

So can willpower be trained like a muscle? A meta-analysis of 33 training studies (158 effect sizes) that had people practise self-control repeatedly reported a small to medium effect (g = 0.30), but the effect was larger in studies where the comparison group did nothing, and in studies with supporters of the muscle theory among the authors. After correcting for bias, the effect shrank to g = 0.13 to 0.24, and there was not enough evidence to conclude that repeatedly overriding impulses is what drives the effect (from the abstract; Friese et al., 2017).

Taken together, the research fits better with designing your day so that you need to hold back less than with straining to build up your powers of restraint. Of the methods below, changing your situation and if-then plans have been tested in experiments; the rest are suggestions in light of the studies above.

First, meet temptations less often. When studying or working, keep your phone in another room or block distracting apps, so that temptations are far away and what you mean to do is close at hand. A student going to the library without a phone was used as an example of a situational strategy (Duckworth et al., 2016a), and students who changed their surroundings to put temptations out of sight said they met their study goals better (Duckworth et al., 2016b). Ways to cut down phone use are covered in the smartphone overuse guide.

Second, decide in advance when, where and what you will do, in the form “if X happens, then I will do Y”. In a meta-analysis of 94 studies, people who planned this way reached their goals to a medium-to-large degree more than people who only set the goal (d = 0.65) (Gollwitzer & Sheeran, 2006; Rozental et al., 2018). A recent analysis of 642 tests found larger effects when plans had a proper if-then format, people really wanted to reach the goal, and they rehearsed the plan (Sheeran et al., 2025). For example, you could decide what to do at the moment temptation strikes: “If I crave a late-night snack, I will drink a glass of water and brush my teeth.” This example was not itself tested in the studies.

Third, turn things you need to do often into habits by repeating them at the same time and in the same place. Habits were, after all, what people with good self-control relied on (Galla & Duckworth, 2015). Practical ways to build habits are in the habits guide.

Fourth, do not take feeling drained as proof that your willpower has run out. Tiredness is a real feeling, but the evidence that it means you are out of fuel is weak, and you do not need sugary food to top up your willpower (Inzlicht et al., 2014; Vadillo et al., 2016). On a tiring day, rather than giving up on the goal, you could shrink the first step until it is very small, and sometimes rest is what you need. This is a suggestion in light of the studies above, not a method tested in research.

Finally, before putting it all down to a weak will, check whether something else is going on. If you have been short of sleep for a long time, if a state of not wanting to do anything has gone on for a while, or if focusing and controlling impulses have been hard in many situations since childhood, you may need a different kind of help than willpower. The insomnia, lack of motivation and adult ADHD symptoms guides cover each of these.

Q. Am I just a weak-willed person? A. People do differ in self-control, and on average those differences are linked to many life outcomes (Moffitt et al., 2011). But people with good self-control, too, often relied on habits rather than effortful resistance (Hofmann et al., 2012; Galla & Duckworth, 2015), and self-control could change as people grew up (Moffitt et al., 2011). When things are not going well, check whether temptations are close at hand before blaming yourself.

Q. Does eating something sweet restore willpower? A. A 2007 study reported that a glucose drink removed the drop in self-control (Gailliot et al., 2007), but an experiment followed in which merely rinsing the mouth worked while blood glucose did not rise (Molden et al., 2012), as did an analysis finding the glucose research weak overall (Vadillo et al., 2016). Small experiments (62 to 154 people) also found that a sugary drink improved self-control only in people who believed willpower is limited (Job et al., 2013). There is little evidence for taking sugar to help your willpower.

Q. Can willpower be trained like a muscle? A. In a meta-analysis of self-control training studies, the average effect was g = 0.30, but it shrank to g = 0.13 to 0.24 after correcting for bias, and what produced the effect was unclear (Friese et al., 2017). Rather than only practising restraint, also try changing your situation and building habits (Duckworth et al., 2016b; Galla & Duckworth, 2015).

Q. Isn’t the study showing that judges grow harsher before lunch proof that willpower runs out? A. A 2011 study is often cited in which, across 1,112 Israeli parole rulings, favourable decisions fell from about 65% just after a break to nearly zero before the next one (Danziger et al., 2011a). Critics pointed out that cases were not heard in random order and that prisoners without a lawyer were usually heard last (Weinshall-Margel & Shapard, 2011), and the original authors replied that their results held when legal representation was added to the analysis (Danziger et al., 2011b). A 2016 simulation showed that simply not starting favourable rulings, which take longer, just before a break could produce a similar pattern and concluded that the original study overestimated the effect, while adding that this cannot account for all of the data (Glöckner, 2016). So the effect was probably overstated rather than fully explained, and since the study analysed rulings rather than measuring anyone’s self-control, it is weak evidence that willpower runs out. The details are in the decision-fatigue part of the why deciding can be so hard guide.

Q. Does believing that “willpower is unlimited” help? A. There is a study in which students who believed this procrastinated less and earned higher grades in busy periods, but it looked at links (Job et al., 2015). The experimental finding that this belief prevents ego depletion was not confirmed in a preregistered replication (Carruth et al., 2023).

Q. Does mind.io have a willpower or self-control test? A. No. If you want to see five personality traits as scores, including conscientiousness, which falls under the umbrella of self-control, you can take the Big Five test. It does not measure how much willpower you have left.

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