- Octreotide
- Ofloxacin
- Olanzapine
- Olmesartan Medoxomil
- Olopatadine
- Olsalazine
- Omalizumab
- Omeprazole
- Ondansetron
- Opium
- Oprelvekin
- Orlistat
- Orphenadrine
- Oseltamivir
- Oxacillin
- Oxaliplatin
- Oxandrolone
- Oxaprozin
- Oxazepam
- Oxcarbazepine
- Oxiconazole
- Oxybutynin
- Oxycodone
- Oxymetholone
- Oxymorphone
- Oxytetracycline
- Oxytocin
Also see:
- ..Optivar(2)
- ..Organidin(2)
- ..Ortho-Cept(1)
- ..Orthovisc(1)
- ..Oxsoralen(1)
- ..Oxyir(1)