How does medical cannabis affect blood pressure?

What is Blood Pressure?

Blood pressure is the force with which blood moves through the body. It is created by the heart as it pushes blood out through contraction and by the differences in pressure between the heart and smaller blood vessels. 

Blood pressure is a vital bodily function, responsible for moving blood (and the nutrients, oxygen, and white blood cells within) to the different areas of the body. It is also essential in carrying waste products through the liver and kidneys. At normal levels, blood pressure facilitates the proper flow of blood from the heart to the body’s other organs and arteries. 

What is “Normal” Blood Pressure?

Blood pressure is measured using two numbers (e.g., 120/80). These numbers represent the systolic pressure (the top number) and the diastolic pressure (the bottom number). 

Both of these numbers are measured in millimetres of mercury (mmHg) using a sphygmomanometer. Systolic pressure (the top number) is the amount of pressure in the arteries during the contraction of the heart muscle. Diastolic pressure refers to the blood pressure when the heart is between beats. 

“Normal” blood pressure can depend on a number of factors; however, according to the British Heart Foundation, it is usually considered to be between 90/60 mmHg and 120/80 mmHg for people below the age of 80. For those aged 80 years and older, the ideal blood pressure is considered to be lower than 150/90 mm Hg.

The Dangers of High Blood Pressure

High blood pressure is considered to be a reading of 140/90 mmHg or higher.  Also known as hypertension, it is the most significant cause of premature death worldwide. 

When blood pressure is too high, it places extra strain on the heart, blood vessels, and other organs, including the brain, kidneys, and eyes. This can increase the risk of a number of other serious health conditions, including:

• Heart disease
• Heart attacks and strokes
• Heart failure
• Peripheral arterial disease
• Kidney disease
• Vascular dementia

Hypertension can also cause a number of other symptoms, such as nosebleeds, morning headaches, vision changes, and buzzing in the ears. A number of factors have been linked to raised blood pressure, including lifestyle choices, such as having a poor diet (being overweight, not eating enough fruit and vegetables, eating too much salt), not doing enough exercise, drinking large amounts of alcohol and smoking. 

Genetics and age have also been linked to high blood pressure. Being over the age of 65 or having a relative with high blood pressure could put you at higher risk of having it, too. The condition is also more prevalent in people of Black African and Caribbean descent and those living in deprived areas. 

What About Low Blood Pressure?

Some people may have low pressure - considered to be a reading of less than 90/60 mmHg. While low blood pressure (hypotension) doesn’t always cause symptoms, it may require treatment when it does. Symptoms can include: 

• Dizziness or lightheadedness
• Feeling sick or weak
• Blurred vision
• Fainting
• Confusion

Like high blood pressure, low blood pressure can be associated with certain medical conditions, such as diabetes, as well as some medicines. If medication is the cause of hypotension, your doctor may alter your dose or change your medicine. Blood pressure can also become lower during pregnancy.

Medical Cannabis and Blood Pressure

Despite being consumed by humans for thousands of years, the link between cannabis and blood pressure is still unclear. While some studies indicate that cannabis use can raise blood pressure, others suggest the opposite may be true. However, more recent studies suggest that the answer may not be straightforward either way.

Does Cannabis Raise Blood Pressure?

Some research suggests that THC, the most common psychoactive compound found in the cannabis plant, may cause an immediate increase in blood pressure. This may be linked to an increased risk of heart attack immediately after cannabis use, particularly in people with existing heart problems. 

However, much of the current evidence linking cannabis use to cardiovascular problems is based on reports from individuals who smoke the drug. This makes it hard to separate the effects of carcinogens and irritants that may be present in cannabis smoke - which is often consumed alongside tobacco - from the effects of cannabinoids and other active cannabis compounds. 

Can Medical Cannabis Lower Blood Pressure?

Several studies have indicated that long-term cannabis use may be associated with lowered blood pressure. For example, a 2023 study assessed questionnaire responses from 91,161 UK citizens from the UK Biobank to examine gender-stratified associations between cannabis use and blood pressure levels. 

They found that lifetime heavy cannabis use was associated with decreases in systolic and diastolic blood pressure, and pulse pressure in both men and women. However, the authors of the study note that the differences in blood pressure between heavy cannabis users and “never users” were too small to recommend adopting cannabis therapy for blood pressure modulation into clinical practice. 

A 2021 study found similar effects. Among older adults, medical cannabis use was associated with a reduction in 24-hour systolic and diastolic blood pressure following three months of treatment. 

CBD and Blood Pressure

There is some evidence that CBD - another common but non-intoxicating cannabinoid - may reduce blood pressure. For example, a 2017 crossover study found that a single dose of CBD reduced resting blood pressure and blood pressure increases due to stress in healthy volunteers, compared to placebo. Again, however, more research is needed to determine whether this effect could be clinically useful in patients with hypertension. 

Final Thoughts

Research into the effects of cannabis on blood pressure is expanding; however, more evidence is required to understand how the effects of different cannabinoids and consumption methods may vary. Furthermore, the mechanisms through which cannabis may impact blood pressure and cardiovascular health require further assessment. 

While current evidence indicates that long-term medical cannabis use may be associated with a reduction in blood pressure, it remains vital that healthcare providers continue to monitor blood pressure and other factors throughout patients’ treatment to ensure the safe and effective use of cannabis-based medicines.