- oats
- octaphonium chloride
- oestradiol
- oestradiol valerate
- oestradiol valerate + norethisterone
- oestriol
- ofloxacin
- oil of amber
- oleoresin capsicum
- oleoresin of capsicum
- oleum
- oleum citri
- oleyl alcohol
- olopatadine
- olsalazine
- omeprazole
- ondansetron
- onopordon
- opium tincture
- orciprenaline
- orciprenaline + bromhexine
- orotic acid
- orphenadrine
- oxaprozin
- oxatomide
- oxazepam
- oxethazaine
- oxybenzone
- oxybuprocaine
- oxybutynin
- oxymetazoline
- oxymetazoline hydrochloride
- oxytetracycline
- oxytetracycline + hydrocortisone
- oxytetracycline + hydrocortisone + polymyxin b