Nopalea is an alternate genus name for one type of prickly pear cactus, as Wikipedia explains. While nopalea, or prickly pear, is generally safe to eat, it can cause diarrhea, nausea and bloating, WebMD points out.
Further side effects of prickly pear ingestion include headache and increased amounts of stool. Ingestion of prickly pear as food is considered safe, according to WebMD. Ingestion of the various parts of the prickly pear plant, including the leaves, flowers and stems, as medicine is possibly safe as well, as is prickly pear extract taken medicinally in appropriate amounts.
Women who are pregnant or breast-feeding should avoid ingesting prickly pear cactus in any form because little is known about its effects on developing fetuses or infants. Diabetics should monitor their blood sugar regularly if taking prickly pear cactus, since it may lower blood sugar, WebMD recommends. This tendency to make it difficult to control blood sugar also makes use of prickly pear potentially dangerous during surgery. Anyone scheduled for surgery should stay away from prickly pear for two weeks before a procedure.
Prickly pear may be effective in single doses for lowering blood sugar levels in diabetics, states WebMD; however, research hasn't yet shown whether this effect lasts over a long period. Prickly pear also appears to be effective for reducing the dry mouth and nausea of hangover.