Blackmores bio magnesium is a one-a-day combination magnesium formula which helps prevent muscular cramps and spasms and helps prevent magnesium deficiency. Magnesium is essential for normal muscle function.why use: • may assist prevention of muscle cramps and spasms • great for people who exercise regularly always read the label. Use only as directed. If symptoms persist see your healthcare professional. Vitamin supplements may only be of use if dietary intake is low.