Urine drug test may boost adherence to blood pressure medications, UK trial suggests

by Mike Addelman, University of Manchester

edited by Lisa Lock, reviewed by Robert Egan

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The largest-ever U.K. trial of a urine test used across the NHS to spot when patients skip their medication has shown it may improve adherence to treatment. Led by researchers at the University of Manchester and Manchester University NHS Foundation Trust (MFT), the study investigated the efficacy of a urine test that detects the presence or absence of blood pressure-lowering medications—known as chemical adherence testing, or CAT.

They tested the hypothesis that the test would help with regular administration of blood pressure-lowering medications and bring patients' blood pressure under control after the results were discussed with them.

Known as the OUTREACH study, it was the largest randomized trial of its kind, bringing together 12 recruitment centers in the U.K. The study is published in The Lancet Primary Care.

CAT uses a special technique called liquid chromatography–mass spectrometry to detect specific drugs or their metabolites in blood or urine samples. It is mainly used in hospital hypertension and renal/cardiology clinics when doctors want to verify medication adherence in patients with resistant hypertension—the medical name for high blood pressure.

The researchers recruited 130 adults with hypertension who were taking at least two blood pressure medicines but were found to be nonadherent after their urine was tested using CAT. Participants were randomly assigned either to receive their CAT results alongside a personalized discussion about why they were missing doses, or to continue with usual care.

After a median follow-up of nearly three months, average systolic blood pressure—the pressure in your arteries when the heart contracts and pumps blood out—was not significantly different between the two groups.

While the adjusted systolic blood pressure in those who received the CAT intervention was 5 mmHg lower than in the standard-of-care group, this difference did not reach the level of statistical significance.

Those who received the intervention, however, became more adherent to the prescribed blood pressure-lowering medications three months after the intervention. This showed a promising sign that it may improve medication adherence.

The findings highlight the challenges of tackling hidden nonadherence, a problem that affects up to one in three people with high blood pressure and costs the NHS millions of pounds in unnecessary tests and treatments.

The authors argue that larger trials are urgently needed to understand whether CAT-based interventions could play a role in improving long-term outcomes for people with hypertension. They also add that the technology may yet prove valuable as part of a personalized approach to managing chronic conditions in which missing medications is common.

The chief investigator of OUTREACH is Maciej Tomaszewski, professor of cardiovascular medicine at the University of Manchester and honorary consultant physician at Manchester University NHS Foundation Trust. He is also integrative cardiovascular medicine co-theme lead at the National Institute for Health and Care Research (NIHR) Manchester Biomedical Research Center (BRC), which partly supported the research.

He said, "Sharing the results of the CAT with the patients and the discussion for the reasons behind missing their blood pressure-lowering medications appears to help in improving adherence. While there was a trend for this improved adherence to favor lower blood pressure, we could not detect a statistically significant signal in blood pressure.

"Hidden nonadherence remains a major and costly problem in hypertension care, and our findings underline the need for larger, longer-term trials to understand where CAT-based approaches might still add value."

Professor Bryan Williams, chief scientific and medical officer at the British Heart Foundation and senior author on the study, said, "High blood pressure is the leading modifiable risk factor for cardiovascular disease in the U.K., where it is associated with 50% of heart attacks and strokes. This means it is crucial that people take medications to treat it as advised by their doctor.

"We hope that this personalized approach to monitoring adherence can help address the many reasons why people may not be taking their medication properly, and support them to do so in future. This study showed signs that this strategy may help improve adherence, but to properly judge its effectiveness, a larger study is needed."

More information

Chemical adherence testing-guided intervention versus standard of care in patients with hypertension who are non-adherent to antihypertensive treatment in the UK (OUTREACH): a multicentre, randomised controlled trial, The Lancet Primary Care (2026).

Key medical concepts

High Blood PressureBlood Pressure MedicinesLiquid Chromatography-Mass SpectrometryHypertension Resistant to Conventional Therapy

Clinical categories

Cardiology Provided by University of Manchester Who's behind this story?

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