The legalization of recreational marijuana in many states and the widespread use of cannabidiol (CBD) brings up many possible questions and concerns regarding the use of these substances in people with and without liver disease. First, let’s define these substances. Marijuana is tetrahydrocannabinol (THC) and THC has a psychoactive effect. CBD, which is more widely sold in stores, does not any have psychoactive effects.
The use of marijuana and liver disease is not well studied. As marijuana stimulates the CB1 receptors, which increases fibrosis and also stimulates CB2 receptors, which decrease fibrosis, the overall effect on hepatic fibrosis is unknown. There have been studies, however, that do show an increase in hepatic fibrosis in patients with hepatitis C, so the use of marijuana in patients with hepatitis C is not recommended. Perhaps the bigger question is the use of marijuana before and after liver transplantation. While there is probably no immediate harm from its use prior to liver transplantation, many liver transplant centers will not offer transplantation to patients who test positive for marijuana, and this testing is performed routinely and regularly while patients are being evaluated once they are listed. After transplantation, there is a concern regarding interference with anti-rejection drug metabolism such as tacrolimus, which may lead to higher and potentially harmful levels of these medications.
The greater unknown is the effect of CBD on people without liver disease. Cannabidiol can be delivered orally, transdermal or inhaled. The differences in potential effects on the liver of these three delivery methods is unknown. There have been several reports of abnormal liver enzymes occurring after CBD use, but the clinical significance is unknown. In general, persistent abnormal liver enzymes related to medication use can lead to liver injury, both acute and chronic. Conversely, CBD has been shown in a single mouse study to improve fatty liver in alcohol related liver disease. Whether this can be extrapolated to humans remains to be seen.
In general, CBD, whether delivered either orally, transdermally or via inhalation, appears to be safe for the liver. The main concern is not liver toxicity, but interference with drug metabolism. To date, CBD, by inhibiting some of the main enzymes within the liver, which metabolize medications, has been shown to increase the levels of certain blood thinners such as coumadin, certain anti-depressants and some cholesterol lowering agents such as statins. Elevated levels of these medications, due to these higher levels, can cause liver injury.
So how should a medical professional respond to the patient question, “Is it safe for my liver for me to use either marijuana or CBD, in any form?” The most responsible answer from your health care provider is: “We just do not have all the data yet and research is ongoing. Many of the CBD products may be helpful for a variety of medical conditions. However, these substances should be used with caution especially if you already suffer from liver disease or take any other medications. It is important to make sure that whatever product you use is pure and does not contain any contaminants. And never, never believe all the claims made on the internet.”