Unblinding for Republic of Ireland

Sites in ROI who have been affected by the ransomware attack on the HSE IT system can call 020 7670 4906 out of hours for emergency unblinding.

Participants in the Add-Aspirin trial take either 100mg aspirin, 300mg aspirin or a matched placebo, once daily for approximately five years. Add-Aspirin is a double-blind trial. This means that neither the participant nor their doctors will know which treatment they have received.

Almost all clinical scenarios can be managed by assuming a trial participant is taking 300mg of aspirin once a day and, if necessary, withholding the trial medication. We only expect unblinding in the Add-Aspirin trial to be necessary in rare clinical circumstances where knowledge of treatment allocation is essential to guide clinical management.
Guidance on a number of anticipated scenarios with specific advice about the need to unblind can be found here.

If unblinding is felt to be clinically essential for a participant in Ireland, any Principal Investigator or authorised investigator at a participating site is able to find out a participant’s treatment allocation through the unblinding process. Where unblinding is being considered, wherever possible, the case should first be discussed with the MRC Clinical Trials Unit (contact details below) or with the trial team at the recruiting hospital (contact details provided on the participant’s Add-Aspirin trial card). A flow diagram of the unblinding process can be found here.

To contact MRC CTU
Phone: +44 (0)20 7670 4892 (during normal working hours)
Email: mrcctu.add-aspirin@ucl.ac.uk

Any Principal Investigator or authorised investigator can directly access treatment information in an emergency using the link below, and entering their email address in addition to the participant’s trial number and date of birth. The participant’s trial number can be found on their Add-Aspirin trial card. Unblinding details will be sent to the email address provided.


In the event that you are unable to contact the MRC CTU and you consider unblinding to be essential for the participant’s immediate management, please proceed to unblind the participant. MRC CTU should be contacted as soon as possible after unblinding.

Contact Details

If you are an individual who is interested in taking part in Add-Aspirin, please talk to your doctor who will be able to consider whether you are suitable for the trial.

For healthcare professionals

Please log into the members area for Add-Aspirin contact details.

Register Interest

For healthcare professionals

If your centre would like to recruit participants to Add-Aspirin, contact us:

Register a participant

From Monday 16th March 2020, to RANDOMISE a participant in the UK please call +44 (0)20 7670 4925, rather than the usual randomisation line.

To RANDOMISE a participant from Republic of Ireland or India only, please use the 'Register a participant' link above to randomise online. Please make sure to press 'Randomise' once logged in to the server.

We have been experiencing intermittent issues with the trial websites. In the event of an emergency unblinding outside of office hours (including over the Easter bank holidays), if the usual unblinding links are not working, please telephone +(0)20 7670 4906 or +(0)20 7670 4892 to reach one of the Trial Managers.

Unblind a participant in the UK

Unblind a participant in the RoI

Unblind a participant in India