Yes, if measured by timed tests. What hypothyroidism mainly does, "by definition", is slow down everything in the organism, including mental functions - so you actually still can think as well as ever, but it takes you longer. read more
Hypothyroidism causes less fuel to be present for the brain to use. Therefore, people with hypothyroidism tend to get brain fog. In this sense, Yes, Hypothyroidism decreases intelligence. read more
Hello again Payne, I remember reading something on "early-onset dementia" ha! mainly joking but it is a possibility. read more