Ketoprofen (KP) and fenofibrate, respectively, anti-inflammatory and hypolipidemiant agents, promote anormal photosensitivity in patients and may induce photoallergic cross-reactions correlated to their benzophenone-like structure. Here, their ability to photosensitize the degradation of biological targets was particularly investigated in DNA. The photosensitization of DNA damage by KP and fenofibric acid (FB), the main metabolite of fenofibrate, and their parent compound, benzophenone (BZ), was examined on a ³²P–end-labeled synthetic oligonucleotide in phosphate-buffered solution using gel sequencing experiments. Upon irradiation at λ > 320 nm, piperidine-sensitive lesions were induced in single-stranded oligonucleotides by KP, FB and BZ at all G sites to the same extent. This pattern of damage, enhanced in D₂O is characteristic of a Type-II mechanism. Spin trapping experiments using 2,2,6,6-tetramethyl-4-piperidone have confirmed the production of singlet oxygen during drug photolysis. On double-stranded oligonucleotides, highly specific DNA break occurred selectively at 5′-G of a 5′-GG-3′ sequence, after alkali treatment. Prolonged irradiation led to the degradation of all G residues, with efficiency decreasing in the order 5′-GG > 5′-GA > 5′-GC > 5′-GT, in good agreement with the calculated lowest ionization potentials of stacked nucleobase models supporting the assumption of a Type-I mechanism involving electron transfer, also observed to a lesser extent with adenine. Cytosine sites were also affected but the action of mannitol which selectively inhibited cytosine lesions suggests, in this case, the involvement of hydroxyl radical, also detected by electronic paramagnetic resonance using 5,5-dimethyl-1-pyrrolidine-1-oxide as spin trap. On a double-stranded ³²P–end-labeled 25-mer oligonucleotide containing TT and TTT sequences, the three compounds were found to photosensitize by triplet–triplet energy transfer the formation of cyclobutane thymine dimers detected using T4 endonuclease V.