Cantharidin is a vesicant, or in other words a chemical that causes irritations and blisters, hence the name blister beetle. Consumption of Spanish fly results in irritation to the urinary tract which in turn can result in sexual stimulation. This is the source of Spanish fly as an aphrodisiac. For all the apparent benefits, cantharidin also can have severe medical consequences and widely is viewed as a poison. The effects range from severe digestive issues, like diarrhea, to internal bleeding and kidney failure to possible death. Symptoms of poisoning can include the following: stomach pain, nausea, vomiting, bloody urine and possible coma.

If a person suspects they have been poisoned with cantharidin, medical physicians are able to run diagnostic tests to check for the presence of the chemical in urine and other body fluids. Unfortunately a direct counteragent is not available for treatment. Medical professionals employ standard oral antipoisoning treatments such as stomach pumping and an IV drip.