Tissue selectivity is a topic in distribution (pharmacology) and property of some drugs. It refers to when a drug occurs in disproportionate concentrations and/or has disproportionate effects in specific tissues relative to other tissues.[1] An example of such drugs are selective estrogen receptor modulators (SERM) like tamoxifen, which show estrogenic effects in some tissues and antiestrogenic effects in other tissues. Another example is peripherally-selective drugs, which do not cross the blood-brain-barrier into the central nervous system and hence are tissue-selective for the periphery.