I got a prescription for vitamin D deficiency and started researching about it. On the way, I found the Coimbra Protocol[1], which evolves around giving high doses of vitamin D (40000-200000 IU) to multiple sclerosis patients.
Same here, and with good results, but a note of warning, according to my doctor 10,000 - 20,000 are considered in the protocol a normal daily supplement for adults with vitamin D issues. Dosages above that require medical supervision (in the form of regular blood and urine analysis). Also at those high doses there are potential negative side effects that must be mitigated (osteoporosis being among them). So please don't just YOLO massive doses of vitamin D.