My Take On It: What I learned from Thomas Hale, R.Ph., Ph.D.


Dr Hale is a professor of pediatrics and associate dean of research at Texas Tech University Health Sciences Center, acting executive director of the InfantRisk Center and author of the bestselling reference book “Medications in Mother’s Milk.”  He is considered one of the foremost experts in the field of perinatal pharmacology and the use of medications by pregnant and breastfeeding mothers. 

In the late fall of 2016, Dr. Hale and his colleague Dr. Teresa Baker received IRB approval for their research study on the transfer of marijuana into human milk specifically examining the kinetics of delta-9-tetrahydrocannabinol (THC) in breastmilk.  In other words, their study seeks to answer the question: How long does the primary psychoactive metabolite found in marijuana (THC) remain in breastmilk after a known quantity of cannabis flower is smoked?

Good research includes community feedback during the planning process and Elephant Circle has enjoyed being involved in the strategic and execution stages of this study.  Both Dr. Hale and Dr. Baker have been extraordinarily responsive to feedback and thoughtful about many elements of the study.  For example, the original study design had breastfeeding parents collect milk for 24 hours, but given further discussion about how hard this could be on breastfeeding parents, the protocol was changed to a collection time of only 6 hours.

Even more importantly, Drs. Hale and Baker listened carefully to concerns about how subjects could participate without risking a visit from Child Protective Services.  They created a protocol that allows breastfeeding parents to participate with complete anonymity and confidentiality.  This was essential to Elephant Circle’s continued involvement, and we are pleased with how the study has been structured to protect subjects.  

The reason for the lecture in Denver

The study is currently in the subject recruitment phase and so Drs. Hale and Baker came to Denver to talk about what is already known about marijuana use during both pregnancy and breastfeeding.  They presented a good summary of the known literature, highlighted there is almost no good research on marijuana use and breastfeeding and answered some critical questions from the audience.  I have summarized what, in my opinion, were the most important concepts found in their talk.

Major concepts from the lecture

1. Cannabis is not concentrated in breastmilk.

The single study that prompted this idea had only two subjects who consumed marijuana 1x and 8x per day respectively, fitting the definition of heavy users.  According to Dr. Hale, the data are “worthless” because there was no attempt to account for previous cannabis use or quantify the amount or timing of the cannabis consumed before the analysis.  In addition, the concept that THC is concentrated in breastmilk isn’t supported by what is known about the physiology of human lactation and human cannabis metabolism. 

·      THC and its metabolites (11-OH-THC and THC-COOH) are cleared quickly from human plasma (when smoked, generally less than 60 minutes – see the graph at the bottom of this post) and are initially redistributed to highly vascular tissues (lung, heart, liver), with 1% initially distributed to the brain 1,2.  Subsequently, the metabolites are distributed to more fatty tissues, primarily adipose tissue, where they are completely metabolized to THC-COOH, the inactive metabolite 1,2.  The fat/brain ratio is 21:1 after 7 days of exposure and 64:1 after 27 days of exposure, highlighting that adipose tissue is the primary long-term repository for the inactive metabolite (THC-COOH) 1,2

·      Breastmilk content reflects plasma content in real-time 3.  This suggests that THC is cleared from breastmilk in the same timeframe as THC is cleared from the bloodstream and THC might be difficult to detect in breastmilk an hour after smoking.

·      There is no obvious mechanism by which THC would increase in the breastmilk after it has been cleared from the bloodstream.

·      Any long-term storage of marijuana metabolites that might occur in breast tissue (which would be very low) exist in the form THC-COOH, the inactive metabolite. 

·      Long-term detection of this inactive metabolite THC-COOH does not reflect the long-term presence of the active metabolite THC 2. 

2. Even though babies are “full of fat,” this does not increase their exposure to the psychoactive metabolite THC.

·        It is more likely that most of the inactive metabolite THC-COOH is stored in the parent’s adipose tissue, not in the adipose tissue of the baby.

·        It is important to differentiate between adipose tissue and fat cells.  Cannabis metabolites are preferentially stored in adipose tissue but not concentrated in particular fat cells (such as those found in breast tissue or breastmilk) 1,2


3. THC is the primary psychoactive molecule in cannabis and it is quickly converted into 11-OH-THC and then into the inactive metabolite THC-COOH.

·      THC-COOH is the molecule used in detection but it is inactive, meaning that it does not create a “high.”

·        Babies might be exposed to the psychoactive THC molecule in breastmilk in the first hour(s) after smoking, but they are not exposed to THC long-term.  Any active THC they consume through breastmilk is most likely quickly converted into inactive THC-COOH. 

·        Even if small amounts are stored in babies’ adipose tissue, they are slowly metabolized and excreted through the urine.  This baby is not stoned during this metabolism as the inactive metabolite is inactive.


4. There is substantial evidence to suggest that endocannabinoids (the cannabinoids that exist in the body already) drive critical elements of blastocyst implantation and exposure to cannabinoids from outside the body (like THC) may increase the risk of miscarriage 4.



1.        Huestis MA. Chem Biodivers. 2007.

2.        Sharma P et al. Iran J Psychiatry. 2012.

3.        Riordin J. Breastfeeding and Human Lactation. 2005..

4.        Fonseca BM et al. Int J Endocrinol. 2013.