Notice of Information: Establishment of a Standard THC Unit to be used in Research
Notice Number:

Key Dates

Release Date:

May 7, 2021

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Issued by

National Institute on Drug Abuse (NIDA)

National Heart, Lung, and Blood Institute (NHLBI)

National Institute of Mental Health (NIMH)

National Cancer Institute (NCI)


Cannabis is a plant containing more than 500 chemicals, and more than 100 cannabinoids. Delta-9-Tetrahydrocannabinol (THC) is the main cannabinoid responsible for the psychotropic and addictive properties of cannabis. Inconsistency in the measurement and reporting of THC exposure has been a major limitation in studies of cannabis use, making it difficult to compare findings among studies. A standardized measure of THC in cannabis products is necessary to advance research by providing greater comparability across studies of both its adverse effects and potential medical uses. The purpose of this Notice is to inform research applicants of a new requirement to measure and report results using a standard THC unit in all applicable human subjects research, beginning May 7, 2021. A standard THC unit is defined as any formulation of cannabis plant material or extract that contains 5 milligrams of THC. This requirement will apply to applications proposing research on cannabis or its main psychotropic constituent THC.

NIH recognizes that the same quantity of THC may have different effects based on route of administration, other product constituents, an individual’s genetic make-up and metabolic factors, prior exposure to cannabis, and other factors. Nonetheless, the goal of this Notice is to increase the comparability of cannabis research studies by establishing a standard unit that can be used to quantify THC exposure, a goal that is a high priority of NIDA leadership and the National Advisory Council on Drug Abuse. Extensive stakeholder input, including a Request for Information to the general public and consultation with experts in the field, led to the selection of 5 mg as a standard unit.

It is not the intent of this Notice to prescribe the quantity of THC that is permissible for use in research projects. Indeed, investigators are free to use more or less than 5mg of THC as appropriate for their study. However, for applicable studies, investigators will be required to report the quantity of THC using the standard unit. Investigators may also report the quantity of THC in other units (e.g., milligrams) as appropriate.

This guidance will apply to applications where THC is a focus of the research. Applicants are responsible for determining whether use of this standard unit is applicable to their research and for determining best approach to applying it in their research applications. A justification should be provided for research that does not propose to use the standard unit.


Please direct all inquiries to:

Scientific/Research Contact(s)

Katia Howlett, PhD
National Institute on Drug Abuse (NIDA)
Telephone: (301) 443-4877

Troy Zarcone, PhD
National Institute on Drug Abuse (NIDA)
Telephone: (301) 443-4577

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