To : Anna Hayward
Re : Marijuana
It is true that in heavy smokers (multiple joints daily) that THC will leak
from their adipose tissue for weeks (maybe up to 4). However, in the
ocassional user, it would be much less. The mean terminal half-life is 25-
57 hours in non-users. Marijuana tends to be sequestered in peripheral
compartments with a hugh volume of distribution of 10 L/kg, which is
absolutely enormous.
THC does enter milk rather easily, but due to low concentration in the
plasma, the absolute dose to the infant is extremely low. Further, while
the absolute oral absorption is complete, a little discussed secret is that
THC is actually largely sequestered in the liver, so little actually reaches
the plasma compartment (which is why people smoke it rather than ingest it
orally). So the milk:plasma ratio of about 8 does not equate to a large
"clinical" dose of the drug at all.
So, lets be clear. If the mom smokes marijuana ocassionally, she should
expect that only small levels will be transferred to the infant, probably
subclinical, which is why the studies show no developmental abnormalities.
However, it should also be clear, that the infant will probably receive
enough drug to be 'drug screen positive' for some time. We don't actually
know if this would be 3 days, a week, or a month, it would totally depend on
the mothers' dose of marijuana.
So, while none of us should support marijuana (or alcohol ) use in
breastfeeding mothers, we should not get overly strident when it does occur
in our clients.
Finally, just for your own information, I will be giving a 1.5 hour lecture
on Drugs of Abuse in Breastfeeding Mothers at ILCA this year. We'll go over
all of the typical drugs, and their breastfeeding kinetics...so join me.
Regards
Tom Hale, Ph.D.
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