insecticide levels remain in the insect to exercise their lethal effect. An important consequence of this property is that, by enhancing the activity of a given insecticide, less may be used to achieve the same result. PBO does not appear to have a significant effect on the MFO system in humans. PBO is found to be an efficacious, low-potency, neutral antagonist of G-protein-coupled CB1 receptors. Other synergists for pyrethroid insecticides include Sesamex and "Sulfoxide" (not to be confused with the functional group). Regulatory PBO is regulated in the United States and some other countries as a pesticide, even though PBO does not have this property. The United States Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), the law that gives United States EPA its authority to regulate pesticides, includes certain synergists in its definition of a “pesticide” and is thus subject to the same approval and registration as products that kill pests, like the insecticides with which PBO is formulated. Pesticide registration is the process through which United States EPA examines the ingredients of a pesticide, where and how the pesticide is used (e.g., whole room fogger, crack-and-crevice, etc.), and the specific use pattern (amount and frequency of its use). United States EPA also evaluates the pesticide to ensure that it will not have unreasonable adverse effects on humans, the environment and non-target species. The United States EPA must register pesticides before they may be sold or distributed in the United States. Registration is required for the pesticide itself, as well as for all products containing it. The World Health Organization recognizes the public health value of PBO when used in conjunction with the synthetic pyrethroids deltamethrin or permethrin used in mosquito nets. Hazard assessment Numerous toxicology studies have been conducted over the past 40 years on PBO examining the full range of potential toxic effects. These studies were conducted in accord with regulatory requirements put forth by the United States EPA or other international agencies. Many were conducted following United States EPA Good Laboratory Practices (GLPs), a system of processes and controls to ensure the consistency, integrity, quality, and reproducibility of laboratory studies conducted in support of pesticides registration. The following types of studies have been conducted in support of PBO registration: Acute toxicity studies Acute toxicity studies are designed to identify potential hazards from acute exposures. The studies usually employ a single or a few high doses over a