What happens if you leave giardia untreated?

Get treated: Why would you even think about not being treated? Treatment is very easy (including some single-dose options) and giardiasis is much worse than any possible side effects. Probably your immune system would clear giardia, but not necessarily; some infections may persist indefinitely. Symptoms probably would eventually improve, even if the infection continues, but it might take weeks or months.

Giardia Lamblia: Giardiasis is a waterborne illness caused by Giardia parasite. Sx's – there may be no sx's or diarrhea, oily floating stool, gas, nausea & abdominal cramps. If untreated it can cause bloody diarrhea, dehydration & weight loss. Diagnosis- via blood test for antibodies & checking stool samples for parasites. Tx can include metronidazole, tinidazole & nitazoxanide.