magnesium citrate oral laxative solution is now only sold with sucralose, which is the devil.

how to make your own magnesium citrate solution
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magnesium molecular weight: 24
magnesium oxide molecular weight: 40
citrate molecular weight: 192
lemon juice acid content: 6 percent

units '40/(192+24)'
= 0.185 grams MgO per gram citrate

ignoring hydrogen, we have
units 0.06 * 1000 = 60 grams citrate per liter lemon juice

if making magnesium citrate solution from lemon juice:
units '24/(192+24)*.06*1000'
= 6.66 mg elemental magnesium per ml

to balance equally:
units '40/(192+24)*.06*1g/ml*1000ml' = 11.1 g MgO

but we want it slightly acidic so let's call it 10g MgO per liter of lemon juice

or about 3 teaspoons of MgO powder per liter of lemon juice

USP oral laxative is 1.745g/floz in a 296ml bottle
units '24/(192+24)*1.745g/floz' mg/ml
= 6.55 mg elemental magnesium per ml

to make 300 ml of USP strength solution:
40/(192+24)*1.745g/floz*300ml = 3.28g MgO
192/(192+24)*1.745g/floz*300ml = 15.7g citric acid
300-3.28-15.7 = 281g water

again we want it slightly acidic so let's call it 3g of MgO and 15g citric acid

this is about 1 tsp of MgO powder and 3 tsp of granulated citric acid


add half the water, and microwave until hot. shake and stir. 
wait until it's clear and add the rest of the water.
keep it in the fridge so it doesn't go bad.

i take 2 tablespoons a day with diluted grape juice and i'm not dead yet.