Is More CBD Better? Dosing and Drug Interactions (Post 1 of 2)

There is a growing trend in the industry to make super concentrated CBD products.  The public may also be confused with the idea that more is better.  CBD has many healthful benefits, but higher doses don’t always have the same therapeutic effects, which I’ll save for another post.  One thing to keep in mind is that along with its potentially therapeutic effects, CBD interacts with many drugs, so it can adversely affect the action of other medications that people may be taking.  Drug interactions are particularly important for people taking high doses of CBD concentrates/isolates who are also on life-saving drugs or drugs with narrow therapeutic windows, or for people taking medications that could have potentially dangerous side effects. 


CBD and other plant cannabinoids can interact with many pharmaceutical drugs by inhibiting the activity of certain cytochrome P450 (CYP450) liver enzymes. CYP450s metabolize up to 80% of all medications including CBD.   Because CBD can outcompete other drugs for CYP450 enzymes, it prevents other drugs from being efficiently metabolized.  This means the drugs can build up in the body at levels much higher than may be safe or effective.  CBD is a more potent inhibitor of CYP450 enzymes than grapefruit, which is more widely known to inhibit CYP450s.  There is no clearly established cut-off dose, below which CBD does not interact with other drugs. 

The extent to which CBD behaves as a competitive inhibitor of CYP450 depends on a number of factors including:

1)    the amount of CBD that is taken

2)    the genetic makeup of the individual taking CBD and his/her other environmental and dietary exposures

3)    whether isolated CBD or a whole plant or whole plant extract of CBD is taken

What drugs may be affected by CBD?

1)    CBD may interact with some anti-seizure medications for the treatment of epilepsy. CBD was found to increase blood levels of clobazam, an anticonvulsant, and norclobazam, an active metabolite. One study of children with epilepsy found benefit to adding CBD to the clobazam drug regimen, but also warned of the importance of monitoring blood levels for clobazam and norclobazam in these children.

2)    CBD reduces the metabolism (degradation) of warfarin (a commonly taken blood thinner), thereby increasing its duration of action and effect. Individuals taking CBD should be monitored more closely for blood levels of warfarin, the dosage should be adjusted accordingly as instructed by their doctor.

3)    Chemotherapy drugs are metabolized by CYP450s before they are inactivated or excreted. Therefore, a patient on chemotherapy taking CBD may result in higher blood concentrations of the chemotherapy drug.  Cancer patients should tell their doctors if they are using cannabis.  There are some studies that show that CBD or CBD/THC may actually enhance patient outcomes favorably, but more trials will be needed on this.  While drug interactions are a potential concern, there have been few reports among the many cancer patients using cannabis while undergoing chemotherapy. It is possible that whole plant cannabis, which contains a slew of other health promoting plant compounds, may interact differently than the isolated CBD that is administered in most research studies. Plus, there are other anti-cancer effects of the cannabinoids that may be beneficial to cancer patients.

Here is a list of just a handful of drugs that can also be affected by CBD:

It is recommended that patients taking CBD not take it at the same time as other medications.  However, the effects of CBD on certain medications can last for over 24 hours. Patients may be able to take smaller quantities of CBD (not super high doses as some people do) to prevent drug interactions. If patients are concerned about a particular medication, they should consult with their health care provider.  It could be that their other meds may need to be adjusted (lowered?) or they could be monitored more closely.