Some side effects follow from graviola's areas of bioactivity. Studies on animal subjects have demonstrated that the plant can dilate blood vessels and lower blood pressure, so those whose blood pressure is already low, or are already on medication to reduce hypertension, should consult their physician before taking graviola [source: Wright]. Also, a large dose taken at one time can cause nausea and vomiting [source: Taylor].
Graviola's purported anti-cancer potency comes largely from its ability to reduce the supply of adenosine triphosphate (ATP) to cancer cells. ATP often provides metabolic energy to healthy cells as well, and some nutritional supplements, notably Coenzyme Q10, are known for increasing ATP. For this reason, CoQ10 may neutralize the effect of graviola and they should not be taken together [source: Taylor].
Researchers exploring the mechanisms that graviola uses claim that the acetogenins in the plant can distinguish cancerous cells from healthy cells because cancer cells have a consistently higher level of cellular activity. The acetogenins recognize and selectively inhibit the cancer cells. Pregnant women are advised to avoid graviola because the high energy in the cells of the developing fetus may trigger the botanical's toxic activity [source: Wright]. The plant was also found to stimulate the uterus in an animal study [source: Taylor].
The most detrimental effect attributed to graviola is that it "may cause neural dysfunction and degeneration leading to symptoms reminiscent of Parkinson's Disease" [source: Memorial Sloan-Kettering]. The first study to make this assertion was conducted by French researchers in Guadeloupe, who found an abnormally high presence of atypical Parkinson's amongst a poor population that used graviola for both food and medicine. However, the outbreak of neurological disorders was relatively confined, whereas the popularity of graviola is widespread in the region [source: Wright]. In her book "The Healing Power of Rainforest Herbs," botanist Leslie Taylor acknowledges that graviola seeds and roots contain alkaloids that have shown neurotoxic effects in tests. For this reason, she recommends using the leaves instead [source: Taylor].