Via the Alternatives section at the bottom of the window, filter the drug list if desired.
Select the medication you wish to prescribe as the alternative.
Click Prescribe to confirm your selection.
You will be prompted to confirm the drug quantity and repeats. Modify if necessary and click OK to continue. This prompt will differ slightly, depending on whether you are modifying a limited or regular medication. It is possible to disable the prompt for regular medications via Prescribing Options.