The goal of this clinical trial is to evaluate whether a lower-dose calcium replacement therapy is non-inferior to a higher-dose regimen in preventing symptomatic hypoparathyroidism in patients following thyroidectomy. The hypothesis is:

• lower-dose calcium replacement therapy is non-inferior to higher-dose therapy in preventing symptomatic hypoparathyroidism during the first two postoperative weeks

Researchers will compare patients receiving a lower-dose calcium replacement regimen with those receiving a higher-dose regimen to assess whether the lower dose is not associated with a higher incidence of symptomatic hypoparathyroidism.

Patients who develop post-thyroidectomy hypoparathyroidism are divided into groups for calcium replacement therapy. If they are asymptomatic, they will be scheduled for a follow-up visit at two weeks after surgery. During the follow-up visit, calcium metabolism will be evaluated, and treatment adjusted if necessary.

Inclusion Criteria:

• patients over the age of 18 undergoing surgery involving both lobes of the thyroid gland (thyroidectomy, "near-total" thyroidectomy, subtotal thyroidectomy, and "completed" thyroidectomy)
• Based on the first post-operative day analysis, PTH levels are below the normal range (in our hospitals 1.8-7.8 pmol/l), but not so low (below 1.06 pmol/L) as to require calcium replacement therapy with calcitriol (rocaltrol)

Exclusion Criteria:

• previously diagnosed osteoporosis; the patient is already taking calcium and vitamin D supplements prior to thyroid surgery
• renal insufficiency (eGFR < 30)
• patients with concomitant hyperparathyroidism undergoing simultaneous thyroidectomy and parathyroidectomy for a parathyroid adenoma