Calcium carbonate + D3
This combination pairs calcium carbonate, a mineral salt supplying elemental calcium, with vitamin D3, which the body converts to the hormone that drives calcium absorption from the gut. Together they support the mineral supply for bone and correct dietary or vitamin D shortfall. It is used for bone health and for deficiency of either component.
Calcium carbonate needs stomach acid to dissolve, so it is taken with food, and the body absorbs calcium better in smaller portions than all at once, which is why the daily amount is split. In the gut calcium binds levothyroxine, ferrous sulfate and the antibiotics doxycycline and ciprofloxacin and stops them being absorbed, so a couple of hours' separation from other medicines is the rule. More calcium passing through the kidneys means more calcium in the urine and a higher risk of stones, particularly for anyone who has had one. Total and ionised calcium along with vitamin D are the markers used to confirm the level is right rather than excessive.
Flank or back pain, blood in the urine, or pain on passing urine suggest a stone and need assessment. Nausea, constipation, unusual thirst, confusion or marked fatigue can reflect calcium that has climbed too high, and are reasons to see a doctor.
Reference information, not medical advice. Discuss any change with your doctor.