thyroid underactive thyroid gland Underactive thyroid (hypothyroidism). Underactive Thyroid Gland (hypothyroidism) underactive thyroid thyroid condition Underactive thyroid Underactive thyroid (hypothyroidism) thyroid thyroid the NHS. thyroid Source NHS Choices hypothyroidism thyroid underactive thyroid underactive thyroid (hypothyroidism) thyroid Underactive thyroid (hypothyroidism).