I can understand wanting to protect your kidneys, but I agree, a medication that gives you headaches and isn't well tolerated won't do it, unless he can tell you that it gets better. (for instance, with metformin, most of us have some digestive problems at the start, but this gets better over time, so knowing this, its worth it to stick it out).
Are you also on metformin? THis also has protective effects.
What is your blood pressure when you are on the enelapril? is it in your boots causing the headaches? My husband was prescribed something similar, and he felt so awful on it, it was lowering his bp too much. Even after a month, he hadn't adapted, so went off it, and is using something else his doc recommended.
zen and the art of weight loss, finding the true path of en-lighten-ment