Can I take Cannabis and Clarithromycin together?

Why this happens

Your liver uses a specific enzyme (called CYP3A4) to break down cannabis. Clarithromycin 'switches off' this enzyme, which prevents your body from clearing the cannabis. This leads to a buildup of the drug in your system. Additionally, both substances can occasionally affect your heart rhythm.

What you should do

It is best to avoid using cannabis while taking a course of clarithromycin. If you do choose to use both, start with a much lower dose of cannabis than usual and be aware that the effects will last longer. Seek medical help if you feel your heart racing or feel extremely dizzy.

Important precautions

Heart rhythm disorders (Long QT syndrome)

Clarithromycin can cause serious heart rhythm problems. You must not take it if you have a history of 'Long QT syndrome' or are taking other medicines that affect heart rhythm.

Drug-drug interaction

Clarithromycin is a strong enzyme inhibitor that can significantly increase the levels of cannabis in your blood, increasing the risk of severe side effects like extreme drowsiness, paranoia, or rapid heart rate.

Psychosis or Schizophrenia

You must not use cannabis if you have a personal or strong family history of schizophrenia or other psychotic disorders, as it can trigger or worsen these conditions.

Driving and operating machinery

It is an offence to drive if your ability is impaired by cannabis. Even if you do not feel 'high', the drug stays in your system and can result in a drug-driving conviction.

Food and drink warnings

Alcohol

Drinking alcohol while using cannabis can significantly increase the sedative effects, leading to extreme drowsiness, dizziness, and impaired coordination. It may also increase the levels of THC in your blood, making the 'high' more intense or unpredictable.

Fatty meals

If you are taking cannabis in oral forms (like oils or capsules), eating a high-fat meal can significantly increase the amount of the drug absorbed into your system. This can make the effects much stronger than usual. It is best to be consistent with how you take it in relation to food.

Grapefruit juice

Grapefruit and grapefruit juice can interfere with how your body breaks down clarithromycin. This can lead to higher levels of the medicine in your blood, increasing the risk of side effects like an irregular heartbeat or stomach upset. Avoid large amounts of grapefruit products while taking this antibiotic.

Grapefruit and grapefruit juice can interfere with how your body breaks down certain compounds in cannabis (particularly CBD). This can lead to higher levels of the medicine in your system, potentially increasing side effects.

Using other medicines

Taking multiple medicines? Our Medicines Interaction Checker helps you check whether your prescriptions, over-the-counter medicines, and supplements are safe to take together. Simply search for your medicines to see potential interactions and what to do about them.

Disclaimer

This information is for general educational purposes only and should not be relied upon as a substitute for professional medical advice. Always consult your GP, pharmacist, or another qualified healthcare professional before making decisions about your medications. Individual circumstances may vary, and only a healthcare professional who knows your medical history can provide personalised guidance.