- Octreotide
- Ofloxacin
- Oleandomycin
- Olsalazine
- Omeprazole
- Ondansetron
- Opipramol
- Opium
- Oral Contraceptives
- Orlistat
- Orphenadrine
- Oseltamivir
- Ouabain
- Oxacillin
- Oxaprozin
- Oxazepam
- Oxcarbazepine
- Oxprenolol
- Oxtriphylline
- Oxybutynin
- Oxycodone
- Oxymetazoline
- Oxymorphone
- Oxyphenbutazone
- Oxyphencyclimine
- Oxyphenonium
- Oxytetracycline
