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This resource focuses on side effects and other terms used in medicines information and assessments of medicines. It does not include terms that are used only rarely, nor does it cover most disease states or technical terms.
How to use EMA’s medical terms simplifier
- You can search for a term or click on a letter below to see terms beginning with that letter.
- Each entry contains a short description. For some, a longer or alternative description is available by selecting the term.
- We use ‘< >’ to indicate alternative or optional wording.
EMA’s medical terms simplifier will be updated periodically. For comments or suggestions, you can use our Medical terms simplifier comments form.
O
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Obesity
being very overweight -
Observational studies
studies looking at the effects of medicines as they are used by patients in a real-life setting -
Obstructive sleep apnoea (syndrome)
see apnoea, obstructive sleep -
Ocular
of eye -
Ocular hyperaemia
see hyperaemia, ocular -
Ocular hypertension
see hypertension, ocular -
Oedema
swelling; fluid retention -
Oedema, cerebral
swelling in the brain -
Oedema, macular
swelling in the macula, the central part of the retina at the back of the eye -
Oedema, periorbital
puffy eyes -
Oedema, peripheral
swelling especially of the ankles and feet <due to fluid retention> -
Oesophageal
<gullet> <foodpipe> <tube that leads from the mouth to the stomach> -
Oesophageal stenosis
see stenosis -
Oesophagitis
inflammation of the foodpipe -
Oesophagus
the tube that leads from the mouth to the stomach -
Oestrogen
a female sex hormone -
Oestrogen-receptor negative
where the cancer cells do not have receptors for the hormone oestrogen on their surface -
Oestrogen-receptor positive
where the cancer cells have receptors for the hormone oestrogen on their surface -
Oligo-ovulatory
rarely produces eggs -
Oliguria
low urine output -
Oncologist
cancer specialist -
Opacity
clouding -
Open-angle glaucoma
see glaucoma, open-angle -
Ophthalmologist
eye specialist -
Opioid
a <painkiller><medicine> that is related to morphine -
Opportunistic infections
infections seen in patients with a weakened immune system -
Optic nerve
the nerve that sends signals from the eye to the brain -
Oral mucositis
see mucositis, oral -
Orodispersible
that dissolves in the mouth -
Oropharynx (oropharyngeal)
mouth and throat -
Orphan medicine
a medicine used in rare diseases -
Orthopaedic
relating to the bones -
Orthostatic
on standing or sitting up -
Orthostatic hypotension
see hypotension, postural -
Ossification
bone formation -
Osteoarthritis
swelling and pain in the joints -
Osteoblasts
bone-forming cells -
Osteoclasts
cells that are involved in breaking down the bone tissue -
Osteomalacia
a condition in which bones become soft and deformed -
Osteomyelitis
bone infection -
Osteonecrosis
death of bone tissue -
Osteopenia
reduction in bone strength -
Osteoporosis
a disease that makes bones fragile -
Otitis media
infection of the middle ear -
Ovalbumin
a protein in egg white -
Ovarian cysts
sacs of fluid within the ovaries -
Ovarian hyperstimulation syndrome
when the ovaries over-respond to treatment <causing nausea, weight gain and diarrhoea> -
Ovarian stimulation
fertility treatment where the ovaries are stimulated to release more eggs -
Overall response rate
[used in cancer trials] percentage of patients who have either no sign of cancer or <shrinkage of the tumour><a decrease in the extent of the cancer> after treatment -
Overall survival
[used in cancer trials] how long patients live -
Ovulation
the release of eggs <during the menstrual cycle> -
Oxygen saturation
a measure of oxygen levels in the blood