One possible side effect of drinking Nopalea cactus juice is a headache. Gastrointestinal symptoms such as nausea, gas, diarrhea, bloating or frequent bowel movements are also possible, according to WebMD.
Juice from the Nopalea cactus, also known as prickly pear, contains quercetin, an antioxidant that protects against inflammation in the body, explains Carol Eustice for About.com. Nopalea cactus juice is marketed as a pain reliever for osteoarthritis and other conditions related to inflammation.
While the anti-inflammatory properties of quercetin have been proven in laboratory studies, no research proves they work the same way in people, says Eustice. Quercetin can interact with some medications, including cyclosporine and corticosteroids, notes the University of Maryland Medical Center.