Sure we can open up a healthy debate on the topic.
I'll give you a little back story.
Everyone in the small country town I was living in got this thing following a rain event whereby the local water reservoir/swamp which is surrounded by cattle grazing land broke its banks. We all knew it was Giardia at that time but of course thought it would just go away, and for most it did.
Some people had no symptoms, some had symptoms that lasted a few weeks, and for people like me, lasting problems.
Although we never got the drinking water tested for Giardia, they did test the water for everything else, coliforms etc. which was negative.
It took three trips to the doctor before pathology finally got a positive for Giardia.
This thing caused nightmares for me and forced me to quit my job and leave work. At my worst, recently, I had skin lesions, chronic diarrhea, allergies to all dairy and wheat products (never had before), would sleep for 12 hours through all alarms and wake up feeling like I'd been hit by a truck.
I had tried Tinidazole twice, the Docs here are only allowed to prescribe a single dose of 4 tablets. Each time I felt like a new man in the following days with symptoms unfortunately creeping back after about a week.
It was at this time I decided to take matters into my own hands.. it has been a few weeks and It appears my live stock meds have done the trick..
If I relapse I'll let everyone know.
P.S. The doctors don't want to know about the back story or hear me talk about parasites.. they want to stick a camera up "there" or call it IBS. Pointless IMHO, the definite response to the Tinidazole was confirmation for me. I just needed a stronger and/or longer treatment.