Why can't I run OpenVPN on Windows from a non-admin user account?

There are two reasons:

• Windows does not provide a WHQL-approved method to allow the TAP-Win32 driver to make its virtual device node accessible from a non-admin account.
• OpenVPN needs the ability to add routes to the system routing table. This requires admin privileges.

For more information, see the article How To Run OpenVPN as a non-admin user in Windows by Mathias Sundman.