Post-marketing cases have been reported indicating a potential interaction between ritonavir containing products and levothyroxine. Thyroid stimulating hormone (TSH) should be monitored in patients treated with levothyroxine at least the first month after starting and/or ending lopinavir/ritonavir treatment.
Kaletra Summary of Product Characteristics, AbbVie Ltd, January 2021.

An HIV-infected patient stable on zidovudine, lamivudine and lopinavir/ritonavir commenced levothyroxine following a total thyroidectomy. Routine hormonal tests showed a persistent hypothyroidism defined by an increase in thyroid stimulating hormone (TSH) serum level and a decrease in free serum T4 level (85 mIU/l and 4.8 pmol/l, respectively) associated with clinical symptoms of hypothyroidism. The abnormal results of the thyroid hormonal tests persisted despite the increase in daily dose of levothyroxine up to 225 µg/day and the introduction of liothyronine. On the basis of a possible interaction between protease inhibitors and levothyroxine, the lopinavir/ritonavir-containing HAART was withdrawn. Two months later the TSH and T4 serum concentrations had returned to normal level and remained stable. Following the re-introduction of zidovudine, lamivudine lopinavir/ritonavir, blood tests performed 1 month later showed a recurrence of hypothyroidism with TSH serum level increase to 42 mIU/l.
Dramatic interaction between levothyroxine and lopinavir/ritonavir in a HIV-infected patient. Touzot M, Beller CL, Touzot F, et al. AIDS, 2006, 20(8): 1210-2.