Tirzepatide, marketed as Mounjaro for type 2 diabetes and Zepbound for weight management, is a dual GIP/GLP-1 receptor agonist that reduces appetite and improves glycaemic control. Patients prescribed this medication may wonder about the safety of using cannabis (weed) concurrently. Whilst no direct pharmacological interaction is documented between tirzepatide and cannabis, combining these substances raises important clinical considerations. Cannabis can stimulate appetite, potentially counteracting tirzepatide's weight-loss effects, and may affect blood glucose control. This article examines the evidence, potential risks, and practical guidance for patients using or considering cannabis alongside tirzepatide treatment in the UK.

Understanding Tirzepatide and Cannabis Use

Tirzepatide is available in the UK under two brand names with different licensed indications: Mounjaro for the treatment of type 2 diabetes mellitus, and Zepbound for weight management in adults with obesity or overweight with weight-related comorbidities. For weight management, it is specifically licensed as an adjunct to a reduced-calorie diet and increased physical activity. It belongs to a novel class of medicines known as dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonists.

On the NHS, Zepbound for weight management is restricted to patients meeting specific NICE criteria (TA1026) and is only available through specialist weight management services. Tirzepatide is administered once weekly via subcutaneous injection and works by enhancing insulin secretion in response to meals, suppressing glucagon release, slowing gastric emptying, and reducing appetite—mechanisms that collectively improve glycaemic control and promote weight loss.

Cannabis, commonly referred to as weed, contains numerous active compounds, the most prominent being delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). When smoked or otherwise consumed, cannabis affects the central nervous system, producing effects ranging from relaxation and altered perception to increased appetite (often termed "the munchies"), changes in mood, and impaired cognitive function. In the UK, cannabis remains a controlled substance under the Misuse of Drugs Act 1971, classified as a Class B drug, making recreational use illegal. However, certain cannabis-based medicinal products are available on prescription for specific conditions under tightly regulated circumstances.

Patients prescribed tirzepatide may wonder whether using cannabis—either recreationally or medicinally—poses risks or affects the medication's efficacy. Understanding both substances' pharmacological profiles is essential for making informed decisions about concurrent use and recognising potential health implications.

Known Drug Interactions Between Tirzepatide and Cannabis

Currently, there is no official documented interaction between tirzepatide and cannabis listed in the UK Summary of Product Characteristics (SmPCs) for Mounjaro or Zepbound. Tirzepatide is a peptide-based medication that is metabolised primarily through proteolytic cleavage rather than hepatic cytochrome P450 enzyme pathways, which are commonly involved in drug-drug interactions.

Cannabis compounds, particularly THC and CBD, are metabolised extensively in the liver via cytochrome P450 enzymes (notably CYP3A4, CYP2C9, and CYP2C19). While CBD can inhibit or induce certain enzymes and potentially affect the metabolism of other medications, tirzepatide's peptide structure and metabolic pathway make direct enzymatic interactions unlikely.

However, it's important to note that tirzepatide significantly delays gastric emptying, which could potentially alter the absorption and onset of action of orally administered cannabinoids (such as edibles or CBD oils). This effect might lead to unpredictable timing or intensity of effects from oral cannabis products.

The absence of a documented interaction does not equate to safety or lack of clinical concern. The effects of cannabis on appetite, blood glucose levels, and gastrointestinal function may indirectly influence diabetes management and weight control—key therapeutic goals for patients using tirzepatide. Additionally, limited research exists on the combined use of GLP-1 receptor agonists and cannabis, meaning potential interactions or adverse outcomes may not yet be fully characterised. Patients should be aware that the lack of formal interaction data does not eliminate the need for caution and clinical vigilance when using both substances concurrently.

Potential Risks and Side Effects of Combining Tirzepatide with Cannabis

While direct pharmacological interactions may be minimal, combining tirzepatide with cannabis carries several indirect risks that warrant careful consideration. One primary concern relates to appetite and dietary control. Tirzepatide reduces appetite and promotes satiety as part of its mechanism for weight loss and glycaemic control. Conversely, THC in cannabis is well known to stimulate appetite, potentially counteracting tirzepatide's appetite-suppressing effects. This could undermine weight management goals and complicate diabetes control, particularly if increased food intake leads to higher caloric consumption or poor dietary choices.

Gastrointestinal side effects are common with tirzepatide, including nausea, vomiting, diarrhoea, constipation, and abdominal discomfort, particularly during dose escalation. Cannabis use can also affect gastrointestinal motility and may either exacerbate or mask these symptoms. Some individuals use cannabis to alleviate nausea, but this could obscure important adverse effects that require medical attention or dose adjustment. Patients should be aware of cannabinoid hyperemesis syndrome (CHS), a condition associated with long-term cannabis use that causes persistent vomiting and dehydration. Combined with tirzepatide's GI effects, this could lead to severe dehydration requiring urgent medical care.

Blood glucose fluctuations represent another concern. The effects of cannabis on blood glucose are variable and unpredictable. For patients with type 2 diabetes using tirzepatide, maintaining stable blood glucose is critical, and any factor introducing variability can complicate management. Patients also taking insulin or sulfonylureas with tirzepatide should be particularly vigilant about hypoglycaemia risk.

Cardiovascular effects should be considered. Both tirzepatide and cannabis can increase heart rate. This additive effect could potentially cause palpitations or exacerbate anxiety, particularly in those with pre-existing cardiovascular conditions.

Patients should be alert for warning signs of serious complications including:

• Severe, persistent abdominal pain (possibly radiating to the back or shoulder), which could indicate pancreatitis or gallbladder disease

• Persistent vomiting or inability to keep fluids down

• Yellowing of the skin or eyes (jaundice)

• Chest pain or persistent palpitations

Additionally, cognitive and psychomotor impairment from cannabis may affect a patient's ability to adhere to medication schedules, monitor blood glucose appropriately, or recognise symptoms of hypoglycaemia or other complications. Patients should be aware that combining substances affecting the central nervous system and metabolic function requires heightened self-monitoring and clinical oversight.

Clinical Considerations for Patients Using Both Substances

Patients currently prescribed tirzepatide who use or are considering using cannabis should discuss this openly with their GP or diabetes specialist. Transparent communication enables healthcare professionals to provide individualised advice, monitor for potential complications, and adjust treatment plans as necessary. It is important to disclose all substance use, including recreational cannabis, as this information is treated confidentially and is essential for safe, effective care.

Key clinical considerations include:

• Monitoring glycaemic control: Patients should maintain regular blood glucose monitoring, particularly if cannabis use is frequent or if dietary patterns change. Unexplained fluctuations in glucose levels should prompt review with a healthcare professional.

• Weight management tracking: Regular weight measurements and dietary assessments help determine whether cannabis use is interfering with weight loss goals. If weight loss plateaus or reverses, this should be discussed during consultations.

• Recognising and reporting side effects: Patients should be vigilant for worsening gastrointestinal symptoms, unusual fatigue, dizziness, or mood changes. Any new or concerning symptoms warrant medical review to distinguish between medication side effects, cannabis effects, or potential interactions.

• Maintaining hydration: During episodes of nausea, vomiting or diarrhoea, maintaining adequate fluid intake is essential. If unable to keep fluids down, seek medical advice promptly.

• Adherence to medication schedules: Cannabis-induced cognitive effects may impair memory or routine. Patients should use reminders or adherence aids to ensure consistent weekly tirzepatide administration.

• Driving and operating machinery: Patients should follow DVLA guidance regarding diabetes medications. Those taking tirzepatide with insulin or sulfonylureas should be particularly aware of hypoglycaemia risk while driving. Do not drive if experiencing symptoms such as dizziness, fatigue, or visual disturbances. Cannabis use impairs driving ability and is illegal; never drive after using cannabis.

• Oral cannabis products: If using oral cannabis products (edibles, oils), be aware that tirzepatide's effect on slowing gastric emptying may alter the onset and intensity of effects. Consider using smaller doses initially and monitor effects carefully.

For patients using cannabis medicinally under prescription, coordination between prescribers is essential to ensure all treatments are compatible and appropriately monitored.

If experiencing severe symptoms (persistent vomiting, severe abdominal pain, chest pain), contact NHS 111 for urgent advice or call 999/attend A&E in an emergency.

UK Medical Guidance and Regulatory Perspective

In the UK, NICE guidance for type 2 diabetes (NG28) and obesity management (TA1026) does not specifically address cannabis use in conjunction with GLP-1 receptor agonists like tirzepatide. For weight management, NICE TA1026 restricts NHS use of tirzepatide (Zepbound) to adults with specific BMI thresholds and weight-related conditions, delivered through specialist weight management services alongside diet and physical activity interventions.

The MHRA has not issued specific warnings regarding tirzepatide and cannabis interactions, reflecting the current lack of evidence for direct pharmacological interactions. However, healthcare professionals are encouraged to counsel patients on all potential factors that may influence treatment outcomes, including recreational substance use.

NHS guidance on diabetes management stresses the importance of stable dietary patterns, regular physical activity, and avoidance of substances that may impair self-care or glycaemic control. Recreational cannabis use, being illegal in the UK, is not endorsed, and patients should be aware of the legal implications alongside health considerations.

For patients prescribed cannabis-based medicinal products (such as those for epilepsy, chemotherapy-induced nausea, or chronic pain), prescribers should be informed of concurrent tirzepatide use. Coordination between specialists ensures that all treatments are monitored appropriately and that any emerging concerns are addressed promptly.

When to seek medical advice:

• Severe or persistent abdominal pain (especially if radiating to back or shoulder)

• Persistent vomiting or inability to keep fluids down

• Yellowing of the skin or eyes (jaundice)

• Chest pain or persistent palpitations

• Unexplained changes in blood glucose levels

• Difficulty adhering to medication or diabetes management plans

• Concerns about substance use or mental health

For urgent concerns, contact NHS 111 for advice. For emergencies (severe pain, persistent vomiting with dehydration, chest pain), call 999 or go to A&E.

Patients should contact their GP or diabetes care team if they have questions or concerns about using tirzepatide alongside cannabis. Open, non-judgemental dialogue with healthcare professionals is essential for optimising treatment outcomes and ensuring patient safety.

If you experience side effects from tirzepatide, report them to the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk or via the Yellow Card app), which helps monitor medication safety.

Frequently Asked Questions