cause of death:
"Hypermagnesemia is an electrolyte disorder in which there is a high level of magnesium in the blood.[3] Symptoms include weakness, confusion, decreased breathing rate, and decreased reflexes.[1][3] Complications may include low blood pressure and cardiac arrest.[1][5] "
"The adverse effects of parenterally administered magnesium usually are the result of magnesium intoxication. These include flushing, sweating, hypotension, depressed reflexes, flaccid paralysis, hypothermia, circulatory collapse, cardiac and central nervous system depression proceeding to respiratory paralysis."
due to laxative action you'll probably shit out all salt u have consumed, so preferable method of the administration is parenteral i.e via IV injection which requires far less dosage than in oral administration and onset of the action is more rapid as drug delivered straight in your circular system. you probably need a dropping bottle of 500ml or sth
lethal dose: "The LD50 values were 206 mg/kg for males and 174 mg/kg for females".
or 12g or 2%(for 500ml)~ solution, though rats and humans are different i would look for 50% concentration as this conc seems as maximum allowed in pharmaceutical products:
"Magnesium Sulfate Injection, USP 50% is a sterile, nonpyrogenic, concentrated solution of magnesium sulfate heptahydrate in Water for Injection. It is administered by the intravenous (IV) or intramuscular (IM) routes as an electrolyte replenisher or anticonvulsant."
also odds of the fail in the case of incompetency in certain medical procedures are very high. u can dismantle a dropping system if body aint fixed properly and fail miserably. look for propofol threads in search bar they should contain how-to to IV drug administration