Less screen time: what controlled studies show

The strongest card: a real randomized trial

In 2025, BMC Medicine published a non-blinded randomized controlled trial with 111 healthy Austrian students aged 18 to 29 who had used their smartphone for at least three hours a day at baseline. Fifty-eight were assigned to use it for no more than two hours a day for three weeks; 53 continued as usual. Screen-time screenshots were uploaded weekly.

The intervention group reduced smartphone use by about 155 minutes a day and showed small-to-medium improvements in stress, depressive symptoms, sleep quality and wellbeing. Those are results of this specific short trial, not a promise about every person or about BACK TO CTRL.

The rebound matters

The between-group difference in smartphone time was still present six weeks after baseline, but not from week seven onward. Use moved rapidly back toward its earlier level once the active restriction ended. That makes the study more useful, not less: a short challenge can create change, but it does not automatically redesign the routine that follows.

Cortisol: the body relaxes measurably

In 2018, researchers assigned 138 active Facebook users either to five days without Facebook or to normal use. The no-Facebook group had lower salivary cortisol afterward, but also lower life satisfaction. This mixed result matters. It tested one social platform for five days, not all smartphone use, and it does not support a simple “less phone equals a happier body” claim.

Sleep: the best documented effect

Objective and self-report studies point especially to screen use in bed. In a JAMA Pediatrics study, interactive in-bed use was associated with less total sleep among 79 adolescents across 323 nights. A separate Norwegian survey of nearly 39,000 students found that every additional hour of in-bed screen time was associated with 59 percent higher odds of insomnia symptoms and 24 minutes less sleep. Both are observational findings.

Attention: two weeks are enough for a difference

In the randomized Castelo study (PNAS Nexus 2025), 90.7 percent improved in at least one of three outcomes after their two-week intervention period: subjective wellbeing, mental health or objectively measured sustained attention. This was a pooled responder figure, not evidence that 90.7 percent improved in all three outcomes.

What this means for you

You do not need to copy either radical intervention. The research supports testing clear boundaries and measuring what happens; it does not prove that any particular protected window or product will produce the same health outcomes. The ctrl key is designed to make selected boundaries easier to repeat. All numbers with sources live in our research library.