Magnesium allievates muscle cramps, high blood pressue and insomnia.

MAGNESIUM

The extent of magnesium deficiency is currently a controversial subject.  Research is currently underway to examine the hypothesis that magnesium deficiency may be a major health problem in the U.S. and around the world.  In the meantime, some physicians are having success in treating a variety of disorders with supplemental magnesium.
Dr. Jonathan V. Wright, a well-known and successful practitioner of alternative medicine says, "If it spasms . . . try magnesium."  He has had success in treating muscle spasms, bronchial spasms, intestinal spasms and spasms of the esophagus with supplemental magnesium.
Supplemental magnesium has also been used to successfully treat cardiac arrhythmias and mitral valve prolapse.  Magnesium is often quite beneficial in treating asthma.  Magnesium also reduces the chances of complications in individuals who suffer a heart attack.  In many individuals with high blood pressure, supplemental magnesium will cause a noticable blood pressure drop. 
In diabetics, magnesium supplements can slow the progress of diabetic retinopathy.
Too much oral magnesium can cause diarrhea.  Milk of magnesia (magnesium hydroxide) and epsom salts (magnesium sulfate) are commonly used as laxatives.  The chance of a diarrhea problem can be minimized by taking smaller amounts of magnesium spaced throughout the day and by drinking plenty of water.
Severe magnesium deficiency may require magnesium to be given by injection.  Many physicians who specialize in preventive or alternative medicine have had great success with giving their patients magnesium intravenously or by injection.
Moderate amounts of oral magnesium usually do not cause problems.  Magnesium aspartate is the most readily absorbed, but should not be used by those who have experienced problems with aspartame (Nutrasweet) or monosodium glutamate (MSG).  Magnesium citrate is also an easily absorbed form of magnesium, and has become widely available during the past few years.

For further information, check the following reference:
McLean, Robert M.,  "Magnesium and its Therapeutic Uses:  A Review. " American Journal of Medicine.  Vol. 96. pp. 63-75.  January, 1994.