Yes i was feeling great after 2 weeks on the 5000IU vitamin D i went and did a blood test to confirm how well i was doing, i was surprised that even after being on it for 2 weeks i still had a mild deficiency I hate to imagine what the level was before i started taking vitamin D. Then after 11 weeks the levels are within normal.
Being a fat soluble vitamin a peak should be reached about 6 weeks into using it.