In Castor, there are two separate randomization permissions: 

• Randomization - a user can randomize patients (participants)
• View Randomization - is necessary to see to which group a participant has been allocated

Each of these rights can be assigned to different roles and sites.

The user with Randomize rights only will see the date of randomization and by whom the randomization was performed, but the allocation and randomization number will remain hidden.

This means that all users who need to be blinded to the group allocation should not have View Randomization rights. 

To unblind the randomization, assign the View Randomization permissions to the user who needs unblinding at the end of the study and due note that this is captured in the audit trail.

Make sure that the forms are also built to preserve the blinding. There should be no questions that are dependent on the randomization group, nor should the outcome of randomization be used in a calculation or summary field. The randomization field in your study will indicate 'Hidden' for users without View Randomization rights.

Read more about how to Define user roles.