Scientists in Denmark have found that mechanical restraint may be associated with a small increased short term risk of blood clots among inpatients at psychiatric hospitals, according to their study published in The BMJ.
Although the absolute risk remains very low, the researchers said the findings support ongoing preventive efforts to reduce the use of mechanical restraint.
People with severe mental illness have an increased risk of blood clots – venous thromboembolism (VTE) – which is likely to be due to several risk factors including existing physical illness and lifestyle factors such as smoking and inactivity.
Where inpatients in psychiatric hospitals are at imminent risk of harming themselves or others, mechanical restraint may be necessary. It typically involves the use of a waist belt, and more rarely, wrist or ankle straps.
Mechanical restraint may increase the risk of VTE due to immobility – a known risk factor. But evidence on the size of this potential risk is limited. The researchers therefore set out to examine the short term risk of VTE after mechanical restraint among inpatients at psychiatric hospitals.
Their findings are based on 24 423 patients aged 18 and over who were admitted to a psychiatric hospital in Denmark between January 2000 and September 2022 and were exposed to either mechanical or chemical restraint (use of sedative medication).
A range of potentially influential factors like age, sex, marital status, education level, admission diagnosis, medication history, and time from admission to mechanical or chemical restraint were taken into account.
A total of 10 208 patients were exposed to mechanical restraint during the study period (median age 40; 68% men). Mechanical restraint was associated with a twofold higher 30-day risk of VTE (3.5 per 1 000 patients in the mechanical restraint group compared with 1.7 per 1 000 patients in the chemical restraint group).
If the observed link between mechanical restraint and VTE risk is causal, the researchers estimate that there will be one additional VTE for every 548 of those subjected to restraint.
This is an observational study so no firm conclusions can be drawn about cause and effect, and the researchers cannot rule out the possibility that other unmeasured factors, such as smoking and body weight, may have influenced their results.
However, they minimised bias by including data from all Danish psychiatric hospitals, providing greater confidence in their conclusions.
As such, they conclude: “Mechanical restraint was associated with an elevated risk of VTE. Although the absolute risk was low, these findings highlight the importance of preventive strategies to reduce the risk of VTE in patients exposed to mechanical restraint.”
In a linked editorial, researchers said restraint may be a modifiable risk factor, but more robust estimates of baseline risk are needed.
Study details
Venous thromboembolism after mechanical restraint in psychiatric hospitals: population based cohort and self-controlled case series study
Jakob Hansen Viuff, Lars Pedersen, Irene Petersen, Jan Vandenbroucke, Søren Dinesen Østergaard, Henrik Toft Sørensen.
Published in The BMJ on 1 July 2026
Abstract
Objective
To examine the short term risk of venous thromboembolism (VTE) after mechanical restraint among inpatients at psychiatric hospitals.
Design
Population based cohort and self-controlled case series study.
Setting
Psychiatric hospitals in Denmark, from 1 January 2000 to 30 September 2022.
Participants
A total of 24 423 inpatients (aged ≥18) exposed to mechanical or chemical restraint at psychiatric hospitals. The self-controlled case series included 1 285 patients with incident VTE occurring during or shortly after a stay in a psychiatric hospital.
Main outcome measures
Cumulative incidence of VTE, weighted by propensity, and risk ratios or differences (including number needed to harm) in the cohort study. Incidence rate ratios in predefined risk periods after restraint were used in the self-controlled case series.
Results
At 30 days after restraint, the cumulative incidence of VTE was 3.5 per 1 000 patients (95% confidence interval (CI) 2.5 to 4.7) in the mechanical restraint group and 1.7 per 1 000 patients (1.0 to 2.6) in the chemical restraint group, corresponding to a risk ratio of 2.07 (1.25 to 3.71), a risk difference of 1.8 per 1 000 patients (0.5 to 3.2), and a number needed to harm of 548 (311 to 1 912). In the self-controlled case series, the incidence rate ratio was 4.49 (3.09 to 6.54) in the 14 days after mechanical restraint compared with baseline periods.
Conclusions
Mechanical restraint was associated with an elevated risk of VTE. Although the absolute risk was low, these findings highlight the importance of preventive strategies to reduce the risk of VTE in patients exposed to mechanical restraint.
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