S-adenosyl-L-methionine (SAMe)

Cited from SAMe Safety

"SAMe is likely safe when taken by mouth in doses of 400-600 milligrams daily for up to two years; when taken by mouth at doses of 800-1,600 milligrams daily for up to 42 days; and when given through IV in doses up to 800 milligrams daily for up to 21 days."