Blocking the mobile internet on a smartphone for 14 days improved sustained attention by an amount roughly equivalent to reversing ten years of age-related cognitive decline, according to a 2025 randomized controlled trial led by Noah Castelo and colleagues, published in PNAS Nexus.1 The participants did not give up their phones. They could still call, text, take photos, and use the web on a laptop. They simply lost the constant pocket-sized pull of mobile data for two weeks.
Mental health and subjective well-being improved alongside attention. People who held to the intervention reported feeling less anxious, less low, and more present in their own lives. The effect on attention was unusually large for a behavioral study, which is why the authors framed it as comparable to undoing a decade of typical decline.1
What the study actually did
The Castelo team recruited 467 adults across the United States and Canada and randomly assigned them to one of two groups. One group installed an app called Freedom that blocked mobile internet on their smartphones, including the app stores, all browsers, and any data-driven app, for 14 consecutive days. The other group installed the same app but the block was scheduled to start two weeks later. Both groups completed the same outcome measures, so the comparison was clean.1
Sustained attention was measured with a gradual-onset continuous performance task, a well-validated test in which participants watch a stream of images and respond to most of them while withholding responses to a rare target. It is sensitive to lapses, the small attentional slips that pile up when a brain is tired or distracted. The blocked group made fewer of these lapses by the end of the 14 days. Anxiety and depression scores fell. Subjective well-being rose. The improvement on the attention task, when scaled against published age curves for the same test, mapped onto roughly ten years of attentional youth. That is the line that has traveled across social media, and it is in the paper.1
The authors are careful. They report an average effect across a large group, with individual variation, in a single trial that has not yet been replicated.
Why blocking only mobile data, and not the whole internet?
This is the design choice that makes the study interesting. Most digital-detox research either yanks the phone away entirely or asks people to limit a single app. The Castelo intervention sits in between. Calls and text messages still came through. Email on a laptop still worked. What changed was the smartphone’s status as a portable doorway to everything at once.1
That nuance matters. A phone that cannot pull a feed in line at the post office is a different object than one that can. Participants did not give up connection. They lost the reflex.
The researchers also tracked what people did with the recovered time. The blocked group reported more in-person socializing, more physical activity, and more time spent outdoors. These are activities with their own evidence base for cognitive and emotional benefit, and the authors propose that part of the attention gain was mediated through them, not the absence of phones alone.1
Does the mere presence of a phone really drain attention?
The Castelo trial sits inside a longer running argument. The original “brain drain” paper by Adrian Ward and colleagues in 2017 reported that simply having a smartphone visible on a desk reduced cognitive capacity, even when it was face-down and switched off. The claim caught on quickly, partly because it was easy to picture, partly because it confirmed a feeling many people already had.
Replications have been mixed. A careful 2020 study by Hartmann and colleagues at the Swiss Distance University Institute used a short-term and prospective memory task and found no evidence that a smartphone on the desk impaired performance.3 A 2023 meta-analysis by Böttger, Poschik, and Zierer pooled the available studies and concluded that the brain-drain effect, as originally described, is small and inconsistent across replications. They argued the field had overstated a real but modest phenomenon.2
So what does the Castelo trial add? It moves the question from “does a phone on the desk hurt right now” to “does living without one for two weeks build something back.” The first is about momentary distraction. The second is about cumulative recovery. Those may be different mechanisms with different evidence behind them, and the new study is a stronger test of the second.1
What “ten years of attention” actually means
The headline number deserves unpacking. Sustained attention declines across adulthood at a roughly predictable rate, with healthy people in their fifties typically scoring lower on continuous performance tests than healthy people in their thirties. The Castelo team scaled their effect against that age curve, and the lift looked, statistically, like the difference between someone ten years older and someone ten years younger.1
That is a vivid framing. It is also a comparison, not a literal rejuvenation. No one’s brain became younger. An intervention that takes two weeks moved a metric by an amount that, in cross-sectional data, takes about a decade of aging to reverse. Large for any behavioral change. Not a guarantee for any one person.
Why might this work? Three plausible mechanisms
The paper proposes a few overlapping reasons, and they line up with older lines of evidence.
The first is reduced switching cost. Every time a notification pulls a person from one task to another, the brain pays a small tax to re-orient. Those taxes add up across a day. Removing the easiest source of switches, the always-available phone, lowers the running total. The Castelo data is consistent with that, although it cannot directly measure switching costs in the wild.1
The second is the rebalancing of time toward attention-restoring activities. Stephen Kaplan’s attention restoration theory and the empirical work that followed it, including a 2008 study by Berman, Jonides, and Kaplan in Psychological Science, showed that walking in a quiet park improved performance on directed-attention tasks compared with walking on a busy urban street.4 If people fill their newly empty fifteen-minute pockets with a walk outside instead of a feed, they are buying small servings of that effect across the day.
The third is exercise. Aerobic activity has its own well-established cognitive footprint. A 2011 randomized trial by Kirk Erickson and colleagues, also in PNAS, found that one year of moderate aerobic exercise increased the volume of the hippocampus in older adults and improved spatial memory.5 Two weeks is too short to produce structural change like that, but the same brain that responds to a year of walking also responds, more modestly, to a single session. Participants in the blocked group reported moving more.1
None of these mechanisms is the whole story. They are plausible partial explanations that fit the data.
What the study cannot tell you
It cannot tell you the effect lasts. The trial ended at two weeks, with a short follow-up afterward. Whether attention stays elevated when the block comes off, and how quickly old habits reassert themselves, is an open question. As the authors put it, this was “a specific two-week intervention,” not a lifestyle prescription.
It cannot tell you the same thing will happen to you. Group averages mask variation, and some participants almost certainly improved more than the headline number, and some less. People whose work depends on constant mobile access may find the design impractical to begin with.
It cannot adjudicate the broader culture-war argument about whether smartphones are good or bad for human attention. That is a bigger question than any single trial can settle, and the brain-drain replication record suggests we should be cautious about sweeping claims in either direction.2
If you wanted to try a softer version
The full Castelo intervention is fairly aggressive: a flat block on mobile internet for 14 straight days. Most readers will not want to do that, and the trial’s design does not tell us which softer versions also work. But several smaller moves are at least consistent with what the study found, and with the older attention-restoration and exercise literatures.1,4,5
One option is to disable mobile data on the apps that pull hardest, while leaving messaging and maps alone. A reader who does not care about their feed in line at the bank can switch off cellular data for a few specific apps and effectively replicate part of the design.
Another is a daily window. Some people block non-essential apps from 8 a.m. to 6 p.m. on weekdays and let the evening be normal. Closer to time-restricted eating than to a fast, and it sidesteps the all-or-nothing trap.
A third is to plan for what fills the empty time. The Castelo participants did not just sit and twitch for two weeks. They walked, met friends, exercised, went outside. If a phone block creates a vacuum and nothing is ready to fill it, boredom can drive a person back to the feed within a day.
How much should this change your behavior?
Honest answer: a little. One randomized trial, however well done, is one piece of evidence. Replication will tell us how robust the effect is across populations, devices, and time. The brain-drain story is a useful caution here. A vivid finding traveled fast and the replication record turned out to be patchier than the headlines suggested.2,3
That said, the underlying ingredients of the Castelo intervention have independent support. Time outdoors, in-person contact, and physical activity all show up across the literature on cognition and mood, in studies older and broader than this one.4,5 If a two-week experiment is what gets a person out for a walk in daylight, the walk is doing some real work, even if the phone block is doing less than the headline suggests.
The honest reading is that this is good news, with caveats. As the post that inspired this article put it, it is “worth considering, not a prescription.” A two-week experiment is low cost, reversible, and produces an answer about your own attention that no group average can.
Common questions about the mobile internet study
Did participants give up their smartphones entirely?
No. They kept their phones and could still make calls, send texts, and take photos. The block was specifically on mobile internet data, including app stores and browsers. Internet on laptops and desktops was untouched.1
Did the attention test really show “ten years” of recovery?
The size of the change on a continuous performance task was scaled against published age norms and corresponded to roughly ten years on that curve. It is a comparison to age data, not a measurement of biological age.1
Was the improvement only about the phone, or about what people did instead?
Both. The blocked group reported more time socializing in person, exercising, and being outdoors. The authors suggest these activities mediated part of the cognitive benefit, alongside any direct effect of fewer interruptions.1
How does this fit with the older “brain drain” claim?
The original brain-drain finding, that the mere presence of a phone reduced cognitive capacity, has not replicated cleanly. A 2023 meta-analysis judged the effect small and inconsistent, and a careful 2020 replication found no measurable cost of a phone sitting on the desk. The Castelo trial tests a different claim, about extended absence rather than momentary presence, and is stronger for that question.2,3
Should I do this?
That is up to you. If you have been feeling scattered and you can spare two weeks, the cost is low and the experiment is reversible. If a flat block is too disruptive, blocking the heaviest apps or installing a daily window may capture some of the same benefit without the friction. Track your own attention while you do it. The most useful data point is your own.
The plain version
A clean trial found that blocking mobile data for 14 days lifted sustained attention, mood, and well-being in a large randomized sample. The mechanism is probably a combination of fewer interruptions and a quiet rebalancing of time toward walking, talking, and being outside, all of which have their own track record in the cognition literature.
It is one trial. It is not a magic fix. Your phone is not your enemy and a two-week experiment is not a verdict. What this paper offers is a useful, testable hypothesis about how a small behavioral change might add up to something that feels, from the inside, like getting a piece of yourself back.
Sources
- Castelo N, Kushlev K, Ward AF, Esterman M, Reiner PB. Blocking mobile internet on smartphones improves sustained attention, mental health, and subjective well-being. PNAS Nexus. 2025. PubMed: 39967678
- Böttger T, Poschik M, Zierer K. Does the Brain Drain Effect Really Exist? A Meta-Analysis. Behavioral Sciences. 2023;13(9):751. PubMed: 37754029
- Hartmann M, Martarelli CS, Reber TP, Rothen N. Does a smartphone on the desk drain our brain? No evidence of cognitive costs due to smartphone presence in a short-term and prospective memory task. Consciousness and Cognition. 2020;86:103033. PubMed: 33137560
- Berman MG, Jonides J, Kaplan S. The cognitive benefits of interacting with nature. Psychological Science. 2008;19(12):1207-12. PubMed: 19121124
- Erickson KI, Voss MW, Prakash RS, et al. Exercise training increases size of hippocampus and improves memory. Proceedings of the National Academy of Sciences. 2011;108(7):3017-22. PubMed: 21282661
