- Ocimum (Clarke)
- Ocimum (Deriker)
- Ocimum canum (Phatak)
- Oenantha crocata (Phatak)
- Oenanthe crocata (Deriker)
- Oenanthe (Boericke)
- Oenanthe crocata (Clarke)
- Olea europaea (Anne Wirtz)
- Oleander (Deriker)
- Oleander (Hahnemann)
- Oleander (Phatak)
- Oleum animale (Boericke)
- Oleum animale (Deriker)
- Oleum jecoris (Boericke)
- Oleum jecoris (Phatak)
- Oleum jecoris aselli (Grandgeorge)
- Oleum manimale (Phatak)
- Ononis (Clarke)
- Onosmodium (Phatak)
- Onosmodium (Vitko)
- Oophorinum (Clarke)
- Ophiophagus hannah (Catherine Sharfstein)
- Opium (Boger)
- Opium (Borland)
- Opium (Clarke)
- Opium (Deriker)
- Opium (Grandgeorge)
- Opium (Hahnemann)
- Opium (Kent)
- Opium (Nash)
- Opium (Phatak)
- Opium (Sankaran)
- Opium (Tyler)
- Opium (Vitko)
- Opium (William H Burt)
- Opuntia (Clarke)
- Oreodaphne (Clarke)
- Origanum (Clarke)
- Ornithogalum umbellatum (Deriker)
- Ornithogalum umbellatum (Tayler)
- Ornithogalum (Borland)
- Oscillococcinum (Grandgeorge)
- Osmium (Deriker)
- Osmium (Mira Valvekar)
- Osmium (Phatak)
- Osmium (Sankaran)
- Osmium (Scholten)
- Ostracion cubicus (Phillips)
- Ostrya (Clarke)
- Ovi gallinae (Clarke)
- Ovi gallinae pelicula (Johnson)
- Oxalicum acidum (Deriker)
- Oxalicum acidum (Kent)
- Oxalicum acidum (Le Roux)
- Oxalicum acidum (Phatak)
- Oxalicum acidum (Vitko)
- Oxydendron (Clarke)
- Oxygen (Joshi)
- Oxygen (Mahesh Gandhi)
- Oxygen (Scholten)
- Oxygenium (Sankaran)
- Oxytocin (Deborah Collins)
- Oxytropis (Clarke)
- Ozone (Shah)
- Ozonum (Rosenberg)