Background: Thyroid function tests (TFTs) are one of the most frequently performed hormonal tests. Abnormal reports are commonly encountered even in the absence of thyroid dysfunction with medication use during testing being an important cause of this anomaly. Knowledge about the effects of different drugs on various components of TFTs will prevent unnecessary referrals, investigation and potentially dangerous therapeutic decisions. Objective: This narrative review aims to provide information to physicians regarding how various medicines can alter results of TFT even in the euthyroid state. Methods: Articles published up to April, 2020 in English language were identified through searches in PubMed and Google Scholar with a search strategy using keywords appropriate to analyze the effects of different medications on thyroid assays. Results: Medications ranging from over-the-counter vitamins to anti-cancer drugs are associated with anomalous TFTs in euthyroid individuals. This occurs through mechanisms of assay interference and alterations in levels or affinity of thyroid binding proteins (TBPs). High-dose biotin can mimic findings seen in thyrotoxicosis by interference with immunoassays utilizing streptavidin-biotin immobilizing systems. Heparin-induced increase in non-essential fatty acid causes displacement of thyroxine (T4) from TBP, effecting an artefactual increase in free hormone levels. Increases or decreases in thyroid-binding globulin (TBG), the key TBG, can cause a corresponding change in total T4 and tri-iodothyronine levels. Estrogen, selective estrogen receptor modulators, 5-fluorouracil, mitotane, clofibrate, heroin and methadone can increase while androgens, anabolic steroids, glucocorticoids, nicotinic acid and l-asparaginase can decrease TBG. Salicylates, frusemide, carbamazepine and phenytoin may displace T4 from TBP, producing a decline in the total hormone levels. Conclusions: Many categories of medications can interfere with analysis of TFTs through different mechanisms. Awareness about these drug-induced TFT fallacies is essential to avoid improper diagnosis and overtreatment of euthyroid patients.