A magnesium salt familiar as Epsom salts, used medicinally and in food-related applications. Dissolved in water it acts as an osmotic laxative, drawing fluid into the bowel to relieve occasional constipation. It also appears in bath salts for soothing soaks and, in purified food-grade form, as a firming agent and brewing aid where regulations permit. Intravenous magnesium sulphate is an important hospital treatment for pre-eclampsia and severe asthma. Oral doses should follow label directions, since excessive intake causes diarrhoea and electrolyte disturbance. People with kidney disease need medical advice before use, as they cannot excrete excess magnesium efficiently.