Moringa leaves have not been found to be toxic. Very extensive health and safety studies conducted at the Noguchi Memorial Medical Research Centre in Ghana determined that Moringa leaf powder has no toxic elements. No adverse side effects from even the most concentrated Moringa diet were observed.
This is, however, a subject that merits further study.
For more information:
Fahey, Jed (2006) Nutritional Benefits, Toxicology, and Health Effects of Moringa Leaf Powder vis-à-vis Treatment of Malnutrition. Moringa and other highly nutritious plant resources: Strategies, standards and markets for a better
impact on nutrition in Africa (conference) Accra, Ghana, November 16-18.