The results of the trial, carried out by the University's Stroke Trial Unit in the Division of Clinical Neurosciences, are being published in The Lancet.
The trial was funded by the Medical Research Council, Efficacy and Mechanism Evaluation (EME) Programme, and BUPA Foundation.
The trial involved 4,011 patients with acute stroke, both ischaemic (blood clot) and haemorrhagic (bleeding). Patients were randomly assigned to receive a glyceryl trinitrate 5mg skin patch (often used in angina patients) or no patch for 7 days. Patients who were already on medication for high blood pressure before their stroke were also randomly assigned to either continue or stop this for 7 days after the stroke.
Leading the trial, Stroke Association Professor of Stroke Medicine Philip Bath, said: "We found that in patients with acute stroke and high blood pressure, treatment with glyceryl trinitrate patches had acceptable safety but did not improve functional outcome. But there seemed to be benefit in patients who were treated very early, within 6 hours of the onset of symptoms. We aim to carry out a further, larger trial testing very early treatment with the skin patch.
"Our results also show that there is no evidence to support the policy of continuing pre-stroke blood pressure-lowering medication in the acute phase of stroke. An adverse effect in the group continuing medication was pneumonia in patients who had difficulty swallowing, perhaps due to inhalation of the medication into the lungs. Furthermore, discharge home, disability and cognition were all less favourable in those who were allocated to continue BP treatment immediately."
Professor Bath added: "Our results suggest that antihypertensive treatment should be continued once a patient who has suffered a stroke is stable and is able to swallow medications safely. But there appears to be no urgency to restart treatment in the first week.
"Some doctors in the emergency department seem to feel obliged to get a stroke patient back on their blood pressure medication as soon as possible, but our trial implies they should not rush it."
Efficacy of nitric oxide, with or without continuing antihypertensive treatment, for management of high blood pressure in acute stroke (ENOS): a partial-factorial randomised controlled trial
The Lancet, doi:10.1016/S0140-6736(14)61121-1