The Government's electronic fit note went "live" in July and GPs are starting to use them instead of the old paper version.
The computer-completed forms will still be printed on one side of A4 and include exactly the same information as handwritten notes, the Government emphasised.
Patients can still request handwritten notes if they prefer.
The intention is that most GP practices will be using them by early 2013, said the Department for Work and Pensions (DWP).
The electronic version also includes a scannable system-generated barcode that contains key information and cannot be altered once printed by the GP.
This, the Government said, would enable the note to be "read" to check that the information it contained matched that of the computer-completed fit note, and would also allow information to be fed into employee record systems.
Guidance on the new fit note can be found on the DWP website.