Hyper- and Hypo-
Hyper means too much or too high; hypo means too little or too low.
What it means
Two prefixes that look similar, sound similar, and mean exact opposites.
- Hyper — above, too much, too high. Hypertension is high blood pressure; hyperthyroidism is an overactive thyroid; hyperglycaemia is high blood sugar
- Hypo — below, too little, too low. Hypotension is low blood pressure; hypothyroidism is an underactive thyroid; hypoglycaemia is low blood sugar
They are genuinely easy to confuse in speech, particularly hyperglycaemia and hypoglycaemia, which are opposite emergencies in diabetes.
In practice
Throughout letters, results and prescriptions.
"Hypo" is also used on its own in diabetes, where "having a hypo" means a low blood sugar episode.
Why it matters
If you are unsure which you were told, ask. The two prefixes point in opposite directions and the treatments are opposite too.
If you have diabetes, know your hypo symptoms and always carry something sugary — this is the one place where confusing the two is dangerous.
Clinically reviewed by Dr Mohammad Zubair Khan, GMC 7563469
Last reviewed
August 30, 2026