A 2018 review by the European Food Safety Authority (EFSA) concluded that most uses of neonicotinoid pesticides such as Thiamethoxam represent a risk to wild bees and honeybees.

[12] Thiamethoxam is a broad-spectrum, systemic insecticide, which means it is absorbed quickly by plants and transported to all of its parts, including pollen, where it acts to deter insect feeding.

The compound gets in the way of information transfer between nerve cells by interfering with nicotinic acetylcholine receptors in the central nervous system, and eventually paralyzes the muscles of the insects.

[15] The Food and Agriculture Organization (FAO) of the U.N. assessed thiamethoxam as "moderately hazardous to humans (WHO class III)", because it is harmful if swallowed.

[13]: 20  Thiamethoxam at sublethal concentrations can increase aggressiveness and cannibalism in commercially harvested shrimp such as Procambarus clarkii[16] In bioassays of aquatic organisms, fish, aquatic primary producers, mollusks, worms, and rotifers are often largely insensitive to thiamethoxam concentrations found in surface waters, but insects, such as chironomid larvae are especially susceptible.

[17][18] Sublethal doses of thiamethoxam metabolite clothianidin (0.05–2 ng/bee) have been known to cause reduced foraging activity since at least 1999, but this was quantified in 2012 by RFID tagged honeybees.

[24] The estimated annual use of the compound in US agriculture is mapped by the US Geological Service and showed an increasing trend from its introduction in 2001 to 2014 when it reached 1,420,000 pounds (640,000 kg).

[22] In 2012, several peer reviewed independent studies were published showing that several neonicotinoids had previously undetected routes of exposure affecting bees including through dust, pollen, and nectar; that sub-nanogram toxicity resulted in failure to return to the hive without immediate lethality, the primary symptom of colony collapse disorder; and showing environmental persistence in agricultural irrigation channels and soil.