I have never heard of anyone ever developing cancer who used oleander extract as a preventive Similarly, those who have used oleander to beat cancer have almost never had it return so long as they continue a maintenance dosage.
Dr. Ozel, the inventor or Anvirzel, recommended 1 dose a week as a preventive, but I am not sure that amount was arrived at scientifically. The normal maximum dose when actively fighting cancer is 1 tablespoon taken three times a day (or 5 ml taken three times a day for the Sutherlandia OPC supplement). I would say that a couple of teaspoons two or three times a week would be a good preventive dose.
I take a tablespoon 3 or 4 times a week, and then sometimes go for a few weeks at max dosage amounts. My reasoning is that some cancers can take as long as eight years to gain a foothold and grow to the size of a pinhead or match head and be detectable, and so a couple or three times a year I do the therapeutic doses for oleander and Inositol/IP6 with the idea of wiping out even the remote possibility of cancers being present.
Note: No pill, supplement or any other single item should be relied on without also embracing a healthy lifestyle that includes a good diet and nutrition, cleansing and detox, stress removal, fresh air, plenty of sunshine and plenty of clean fresh water.