I've been taking 3,000IU per day for several years.

My initial symptom was just feeling all the time like I was walking through water. I didn't feel sleepy, just tired all the time. After a blood test, my doctor put me on 50,000IU per week. I immediately felt better. When my prescription ran out I started using OTC vitamins. When I switched doctors, my new doctor wanted to know everything that I was taking. She hasn't commented about it. I'm feeling good. Don't plan on changing.