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Prop 65: Listing of MIBK and Megestrol Acetate
(March 2014)

The California Office of Environmental Health Hazard Assessment (OEHHA) is adding methyl isobutyl ketone (MIBK) and megestrol acetate to the Proposition 65 list of chemicals known to the state of California to cause cancer, birth defects or other reproductive harm. The listing of both chemicals is effective March 28, 2014.

Chemical CAS No. Toxicological Endpoints Listing Mechanism
Methyl Isobutyl Ketone (MIBK) 108-10-1 Developmental Toxicity Authoritative Bodies (U.S. EPA)
Megestrol Acetate 595-33-5 Cancer “Formally required to be labeled or identified”


MIBK has been listed by OEHHA under the authoritative bodies mechanism, based on identification by the U.S. Environmental Protection Agency (EPA) that the chemical causes reproductive toxicity (developmental endpoint). MIBK is commonly used in paint production, pesticide formulations, adhesives, leather finishing, textile coating, specialty surfactants for inks, and as a coating solvent in cellulose- and resin-based coating systems.

OEHHA’s Notice of Intent to List MIBK is available here.

EPA’s Integrated Risk Information System on MIBK is available
here.

EPA’s Toxicological Review of MIBK is available
here.

Megestrol acetate has been added to the list of chemicals known to the state of California to cause cancer under the required identification or labeling listing mechanism. Megestrol acetate has been identified or labeled to communicate a risk of cancer by the U.S. Food and Drug Administration (FDA), and OEHHA has concluded that it is required to be listed under Proposition 65. The FDA-approved labels indicate that when assessing the risk-to-benefit ration of megestrol acetate, consideration must be given to the observations of breast and pituitary cancers from studies in dogs and rats receiving much lower doses of megestrol acetate than the recommended clinical dose for humans.

OEHHA’s Notice of Intent to List megestrol acetate is available
here.

FDA’s approved label is available
here. Relevant information can be found under Carcinogenesis, Mutagenesis, Impairment of Fertility (Section 13.1).

For more information, please Contact TSG.
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