If end users are using OpenVPN client version 2.3.x (or older) on Windows 7 or later, local administrator permissions are required for the user. This is because Windows requires local administrator permissions in order to update the routing table. This required running the OpenVPN client "as administrator" (also sometimes referred to running with elevated privileges).
As of OpenVPN 2.4, local admin permissions are no longer required to launch OpenVPN. OpenVPN 2.4 uses a Windows service wrapper which is installed when OpenVPN is installed, and this is used to update the routing table when connecting.
We strongly recommend running the latest version of OpenVPN, available here, to take advantage of this capability, as well as other security and usability fixes.