Cannabis and Metoprolol (Lopressor)
Generic: metoprolol
Brand names: Lopressor, Toprol-XL
Important Medical Disclaimer
This information is for educational purposes only and does not constitute medical advice. Do not start, stop, or modify your use of Metoprolol or cannabis without consulting your doctor or pharmacist. If you experience adverse effects, seek immediate medical attention. Individual responses to drug combinations vary significantly.
Overview
Metoprolol (Lopressor, Toprol-XL) is a cardioselective beta-1 blocker used for hypertension, angina, heart failure, and post-myocardial infarction prophylaxis. Unlike lisinopril, metoprolol is extensively metabolized by CYP2D6, making it susceptible to CBD-mediated enzyme inhibition. This pharmacokinetic interaction can elevate metoprolol blood levels, intensifying its beta-blocking effects and potentially causing excessive heart rate reduction (bradycardia), hypotension, and fatigue. The interaction is rated moderate because the pharmacokinetic component adds to the pharmacodynamic risk. The cardiovascular effects of cannabis add complexity to this interaction. THC acutely increases heart rate through sympathetic activation, which directly opposes metoprolol's heart rate-lowering effect. This creates a tug-of-war between cannabinoid-mediated tachycardia and beta-blocker-mediated bradycardia, which can be unpredictable and potentially stress the cardiovascular system. Subsequently, as THC's acute effects wear off, the unopposed beta-blockade from elevated metoprolol levels (due to CBD's CYP2D6 inhibition) can lead to significant bradycardia and hypotension. Patients with heart failure or conduction abnormalities are at particular risk. This information is for educational purposes only. Consult your healthcare provider.
How They Interact
Metoprolol is extensively metabolized by CYP2D6, which accounts for approximately 70–80% of its hepatic clearance. The CYP2D6 polymorphism is clinically significant for metoprolol: poor metabolizers (about 7% of Caucasians) have 5-fold higher metoprolol levels than extensive metabolizers. CBD inhibits CYP2D6 (Ki ~1.2–2.7 μM), effectively shifting patients toward a poor metabolizer phenotype. This can dramatically increase metoprolol exposure, particularly in patients who are already intermediate metabolizers. The pharmacodynamic interaction involves opposing and additive cardiovascular effects: THC acutely activates the sympathetic nervous system (causing tachycardia), competing with metoprolol's beta-1 blockade. As THC effects wane, the elevated metoprolol levels from CBD's enzyme inhibition can produce exaggerated bradycardia and hypotension. CBD's own vasodilatory effects further compound the hypotensive risk.
Cannabinoid-Specific Interactions
| Cannabinoid | Interaction with Metoprolol |
|---|---|
| CBD | CBD inhibits CYP2D6, the primary enzyme metabolizing metoprolol. This can substantially increase metoprolol blood levels, mimicking the pharmacokinetic profile of a CYP2D6 poor metabolizer. Elevated metoprolol levels increase the risk of bradycardia, hypotension, fatigue, and heart block. CBD also has intrinsic hypotensive effects that add to this risk. |
| THC | THC has complex cardiovascular interactions with metoprolol. Acutely, THC increases heart rate (opposing beta-blockade), but subsequently can cause hypotension (additive with metoprolol). The push-pull effect on heart rate can be unpredictable and may stress the cardiovascular system, particularly in patients with underlying heart disease. |
| CBN | CBN can lower blood pressure and cause sedation. Combined with elevated metoprolol levels from CBD co-administration, this may contribute to significant hypotension and bradycardia. Patients should be cautious with CBN-containing products. |
Symptoms to Watch For
- ⚠Unusually slow heart rate (bradycardia) or feeling of heart pausing
- ⚠Dizziness, lightheadedness, or fainting upon standing
- ⚠Excessive fatigue or exercise intolerance
- ⚠Cold extremities (hands and feet)
- ⚠Shortness of breath or worsening of heart failure symptoms
Recommendations
- 1Inform your cardiologist or prescribing physician about cannabis use, as metoprolol dose adjustment may be necessary.
- 2Monitor your heart rate and blood pressure at home, especially when starting or changing cannabis products.
- 3Seek medical attention if your resting heart rate drops below 50 beats per minute or you experience fainting.
- 4Be particularly cautious with high-dose CBD products, as the CYP2D6 interaction can substantially elevate metoprolol levels.
- 5If you experience worsening exercise tolerance, increased fatigue, or shortness of breath, contact your physician promptly.
Research Summary
Metoprolol's dependence on CYP2D6 for metabolism is one of the best-characterized pharmacogenomic drug interactions. Studies have shown that CYP2D6 poor metabolizers have 5-fold higher metoprolol AUC compared to extensive metabolizers, with significantly more pronounced beta-blockade. CBD's CYP2D6 inhibition can pharmacologically replicate this poor metabolizer phenotype, an interaction supported by in vitro data and drug interaction predictions from clinical pharmacology databases. While no published clinical trial has specifically examined the metoprolol-CBD interaction, the FDA-approved labeling for metoprolol warns about concurrent CYP2D6 inhibitor use. Case reports have described excessive beta-blockade symptoms in patients combining metoprolol with other CYP2D6 inhibitors. The cardiovascular effects of cannabinoids — including acute tachycardia, subsequent hypotension, and altered cardiac conduction — have been documented in clinical and observational studies. This information is for educational purposes only. Consult your healthcare provider.
Frequently Asked Questions
Can CBD raise my metoprolol levels?
Yes. CBD inhibits CYP2D6, the primary enzyme that breaks down metoprolol in the liver. This can lead to significantly elevated metoprolol levels, causing excessive heart rate slowing, low blood pressure, and fatigue. The effect is similar to what happens in patients who are genetically CYP2D6 poor metabolizers.
Is it dangerous to smoke marijuana while on a beta blocker?
THC in marijuana acutely increases heart rate, which opposes metoprolol's heart rate-lowering effect. This competing cardiovascular stress can be problematic, especially for patients with heart disease. As THC's effects wear off, the residual beta-blockade (potentially intensified by CBD) can cause excessive bradycardia. The combination should be discussed with your cardiologist.
Should my doctor change my metoprolol dose if I use CBD?
Possibly. If you are using significant amounts of CBD (more than 20–25 mg/day), your doctor may need to reduce your metoprolol dose and monitor your heart rate and blood pressure more closely. Do not adjust your metoprolol dose without medical guidance, as abrupt changes can be dangerous.
Are other beta blockers safer to use with cannabis?
Some beta blockers like atenolol and nadolol are renally excreted and not metabolized by CYP2D6, making them less susceptible to CBD-mediated enzyme inhibition. If the interaction is a concern, your doctor might consider switching to a beta blocker with less CYP2D6 dependence. However, the pharmacodynamic cardiovascular effects of cannabis still apply regardless of which beta blocker is used.