Magnesium is found in many supplements — single magnesium products, multivitamin complexes, and formulas for sleep or recovery. If you already take one of these products, it makes sense to add up the total amount of magnesium from all sources and compare it with the recommended daily intake for adults (in the EU it is 375 mg under the food labelling regulation).
Exceeding the norm when taking magnesium from supplements in most cases shows up as digestive upset, but in people with impaired kidney function the situation may be different. Therefore, if you have chronic conditions or doubts about the compatibility of several supplements, it is sensible to check with a doctor or pharmacist.
Boswellia and shilajit are less common in standard multivitamins, so the risk of duplicating these ingredients is usually lower. Nevertheless, if you take several specialised joint supplements at the same time, it is worth checking their compositions for overlaps.