Seems to be readily available under medicaid. But you have to keep you income under $15K or ($10K in non-Obamacare states) to qualify.
Kidney failure in a small set of patients. Typically urine/blood samples are taken for the first few months to check for this. There's some evidence of bone degradation in long term use (think 10+ years) but its mitigated with regular strength exercises. Beyond that not much else the formula has been altered a few times to make it pretty safe to take regularly.
Some people experience gastrointestinal distress from it but that usually passes after a month. If it doesn't they usually just stop taking it.
All of the side effects stop if you stop taking it.