The larger doses of D are the same size gel cap as the 400 unit ones. I don't have a problem with them, although I make sure to take all my supplements with food. I don't tolerate the regular fish oil gel caps, so tolerating the D caps means something. D is also available in tablets, but the gel caps are recommended.
My intolerance for fish oil is probably due to most fish and crab and shrimp being sprayed with sulfite to preserve them right on the boats. If it's not cleaned off adequately during processing, and judging by my reaction it isn't, I get tachycardia. I can eat fish and shrimp just fine if I wash them and cook them myself. If you have a severe intolerance or allergy you could have a problem with D because it's from a fish source.
The formula for raising D level is:
For every 1 ng/mL to be raised you need to add 100 units of D. My level was 18. To raise it to 38 (good on old scale) I needed to add 2000 units. To get it up to 48 (new scale is 50 or even higher) I would need 3000 units more than I was already taking, which was about
1300 units from all sources: vitamin, Calcium supplement, and the extra D I was already taking.