NOW Calcium & Magnesium

Our assessment

The evidence shows that the combination of calcium and magnesium in this product supports bone health and muscle function. Calcium is essential for bone mineralization, while magnesium plays a key role in neuromuscular relaxation and nerve signaling [NIH ODS]. However, we need to be cautious with calcium dosing, as high intakes may carry risks. The data does not specify the exact amounts of each mineral in this particular product, so you should check the label to ensure you are not exceeding recommended daily limits.

How it works

Think of calcium and magnesium as a working pair for your body. Calcium is deposited into your bones to maintain density and strength, and it helps your muscles contract and nerves send signals. Magnesium acts as a natural relaxant, helping muscles release after contraction and supporting calm nerve activity [NIH ODS]. Together, they help maintain the balance your body needs for everyday movement and bone health.

Safety profile

The FDA has received a total of 592,059 adverse event reports across all supplement categories. For calcium specifically, high intakes might increase the risk of heart disease and prostate cancer [NIH ODS]. Very high levels of calcium in the blood and urine can cause poor muscle tone, poor kidney function, low phosphate levels, constipation, nausea, weight loss, extreme tiredness, frequent need to urinate, abnormal heart rhythms, and a high risk of death from heart disease [NIH ODS]. Also, calcium can reduce the absorption of several medications, including bisphosphonates, tetracycline antibiotics, fluoroquinolone antibiotics, levothyroxine, and phenytoin [NIH ODS]. Data on magnesium-specific side effects from this product is not available.

Our recommendation

Check the label for exact dosages of calcium and magnesium. For most adults, aim for no more than 1,000–1,200 mg of total calcium daily from all sources (food and supplements) [NIH ODS]. Take calcium supplements with food and separate them from thyroid medication or antibiotics by at least 2 hours [NIH ODS]. If you have a history of kidney stones, heart disease, or prostate cancer, speak with your doctor before starting this supplement.

Supplement labels contain several key sections regulated by the FDA:

• Serving Size — The recommended amount per dose. Always check this — some products require multiple capsules per serving.
• Amount Per Serving — Shows the quantity of each nutrient in the product, typically in IU (International Units), mg (milligrams), or mcg (micrograms).
• % Daily Value (%DV) — Indicates how much a nutrient in a serving contributes to a daily diet. 5% DV or less is low; 20% DV or more is high.
• Other Ingredients — Lists inactive ingredients like fillers, binders, and capsule materials (e.g., gelatin, cellulose, magnesium stearate).
• Suggested Use — The manufacturer's recommended directions for taking the supplement, including timing and dosage.

Source: FDA Dietary Supplement Labeling Guide