Cantharis is a homeopathic remedy that contains a toxic substance called cantharidin from the insect Lytta vesicatoria, commonly known as the Spanish fly or blister beetle. People use cantharis topically to heal burns and blisters, and orally to treat bladder inflammation (cystitis). Although homeopathic remedies are greatly diluted and generally not associated with side effects, high concentrations of cantharis are poisonous. People should only buy cantharis from a reputable homeopathic practitioner and should not use higher-strength concentrations than those provided in the standard homeopathic remedy.
Urinary Tract Effects
When taken orally in excessive amounts, cantharis may provide toxic levels of cantharidin. Cantharidin can cause burning pain in the urinary tract, frequent urges to urinate, kidney damage and kidney failure. Some individuals consume excessive amounts of cantharis or take illegal higher-strength substances because Spanish fly has traditionally been used as a sexual stimulant. It also can result in priapism, a condition involving a painful erection lasting for several hours. Priapism should be considered a medical emergency because it can lead to permanent damage.
Gastrointestinal Side Effects
Large doses of cantharis or a cantharis remedy that is not properly diluted can also cause severe gastrointestinal effects. These may include abdominal pain, burning sensations in the throat and mouth, difficulty swallowing, severe vomiting and diarrhea. Cantharidin is caustic, and when it is not diluted properly it can cause inflammation, erosion and hemorrhage in the upper gastrointestinal tract.
Blood Disorders
Taking cantharadin can cause abnormal blood clotting, which might result in clots that block blood vessels and the blood flow to vital organs. This abnormal clotting activity eventually decimates the supply of clotting proteins, leading to a reversal of the situation where the individual becomes at risk for severe bleeding. Signs include excessive bleeding from even minor injuries, vomiting blood, rectal bleeding, vaginal bleeding and copious blood in the urine. Cantharadin has also been associated with seizures and cardiac abnormalities.