Here is a long article that has a different method for internal use:
"A therapeutic dose of 9 mg and a maintenance dose of 3 to 6 mg have been used. Boron is not normally available as a supplement. Instead borax or boric acid is being used, 50 mg of borax contains approximately 6 mg of boron and boric acid 8 mg. To measure this amount, dissolve one level teaspoon of borax in one quart of water and take a teaspoonful twice daily with meals."