(131)I, when released in a radiological or nuclear accident as happened recently 
in Fukushima, Japan, may cause thyroid cancer as a long-term consequence. Iodine 
thyroid blocking (ITB) is known to reduce the risk of developing thyroid cancer. 
Potential adverse effects of ITB have not been systematically investigated so 
far. This article summarises the results of a review on adverse effects of ITB 
based on a systematic literature search in scientific medical databases. A 
meta-analysis was not performed as identified studies displayed major 
heterogeneity. The search resulted in 14 articles relevant to the topic, 
reporting mostly on surveys, ecological and intervention studies. Only one study 
from Poland focused on effects (both desired and adverse) of an ITB intervention 
following the Chernobyl accident. All other studies reported on iodine 
administration in a different context. Overall, the studies did not reveal 
severe adverse reactions to potassium iodide in the general public. Since ITB is 
a protective measure only applied in very specific circumstances, scientifically 
sound studies of adverse effects are scarce and consequently the evidence base 
is weak. The assessment of adverse effects of ITB relies on indirect evidence 
from related areas. This study may contribute to ongoing developments in 
pharmacoepidemiology aiming to better quantify adverse effects of medications 
and health care interventions including ITB.