Rheumatoid arthritis (RA) and autoimmune diseases of the thyroid gland (AITD) often occur together. As autoimmune diseases, they share common pathological pathways, reflecting the fact that the treatment of the underlying disease can influence the course of thyroid disorders. The pharmacotherapy of RA is based on the supply of disease-modifying anti-inflammatory drugs with an increasing focus on biologics. This article aims to review the available literature describing the effects of biological treatments on thyroid function. The use of biological drugs may have the potential benefit of regulating the level of anti-thyroid antibodies. On the other hand, tumour necrosis factor-alpha (TNF-a) inhibitors are not indifferent to thyroid function and may increase the incidence of subacute thyroiditis. The coexistence of AITD and RA prompts consideration of the need for routine thyroid screening in RA patients and for RA screening in patients with thyroid disease who report joint problems. Rheumatoid arthritis (RA) and autoimmune diseases of the thyroid gland (AITD) often occur together. As autoimmune diseases, they share common pathological pathways, reflecting the fact that the treatment of the underlying disease can influence the course of thyroid disorders. The pharmacotherapy of RA is based on the supply of disease-modifying anti-inflammatory drugs with an increasing focus on biologics. This article aims to review the available literature describing the effects of biological treatments on thyroid function. The use of biological drugs may have the potential benefit of regulating the level of anti-thyroid antibodies. On the other hand, tumour necrosis factor-alpha (TNF-a) inhibitors are not indifferent to thyroid function and may increase the incidence of subacute thyroiditis. The coexistence of AITD and RA prompts consideration of the need for routine thyroid screening in RA patients and for RA screening in patients with thyroid disease who report joint problems.