The formation of benzene-oxide is widespread in drugs containing a phenyl ring. The bicyclic benzene-oxide metabolite can equilibrate with the corresponding seven-membered oxepine by valence tautomerism. Oxepine can progress to ring opening to yield a reactive alpha, betaunsaturated aldehyde, and trans-trans-muconaldehyde, which are known to have myelotoxicity. The hepatotoxicity of methylenedioxyphenyl containing (Figure ) molecules (safrole, and myristicin) is associated with quinone and its methide tautomer, which are generated during phase I metabolism. CYP1A2 activates safrole into the o-quinone and its methide tautomer, which leads to the inactivation of the enzyme by tightly binding with the enzyme's active site. Photodegradation products of the diketo tautomer of avobenzone have phototoxic effects and cause photoirradiation, restricting its application in sunscreen products. 11