The acetaminophen in Tylenol ( a common over the counter pain and fever medication used by millions of children and adults every day ) is carcinogenic and hepatotoxic.
" There are, however, published data giving clear evidence that paracetamol causes chromosomal damage in vitro in mammalian cells at high concentrations and indicating that similar effects occur in vivo at high dosages. Available data point to three possible mechanisms of paracetamol-induced genotoxicity: (1) inhibition of ribonucleotide reductase; (2) increase in cytosolic and intranuclear Ca2+ levels; (3) DNA damage caused by NAPQI after glutathione depletion. "
"Paracetamol induced sister chromatid exchange in human cells in vivo, and it was aneugenic and induced chromosomal aberrations but not micronuclei in mammalian cells in vivo. It induced DNA single-strand breaks in mice treated in vivo. Paracetamol induced sister chromatid exchange and chromosomal aberrations in human cells in vitro. It weakly induced cell transformation in a mouse cell line. It induced chromosomal aberrations, micronuclei and sister chromatid exchange in mammalian cells in vitro. It did not induce gene mutation, and the results of tests in mammalian cells in vitro for unscheduled DNA synthesis and DNA damage were inconclusive. Overall, paracetamol was genotoxic in mammalian cells in vivo and in vitro. It was not mutagenic to insects but was clastogenic in plant cells."
And here is an entry from the NIH TOXNET database about liver and bladder cancers induced by tylenol.
http://toxnet.nlm.nih.gov/cpdb/chempages/ACETAMINOPHEN.html
Everything including water is toxic under the right conditions.