Hi, Welcome to the forum. Mecalvit contains Calcium carbonate and vitamin D3. Most of the patients take mecalvit quite comfortably while few show symptoms of allergy. We generally prescribe mecalvit with once daily dose of 500mg, for the sake of easy metabolisation. Your symptoms are indicative of the side effect of the medicine. If you are allergic to calcium medications, stop taking those. You have not mentioned since how long you having been taking it. Sometimes it occurs due to drug resistance if taken for a long time and one may have such symptoms. You can change the brand or take calcium syrup to see if you can digest it. Drink a lot of water, re-hydrating fluids, soup and juice to flush the toxic effects out of your body system. Many natural food have a lot of calcium, take bananas, capsicum, apples, brocolli, cabbage, milk, cheese, paneer, yoghurt, tofu, almond, green leafy veggies or turnip, mustard, eggs, many more. Antacids and anti-diarrhoeal medicationa can be of help. Re-visit your treating doctor and get examined, alert him with the allergy from which you have suffering from. Have a nice day, take care.