CHAPTER 5
Medical Risks of Cannabis Use

I am treating patients who are seeking an effective solution to their difficult medical conditions. I rarely see major issues with cannabis use as patients are using medical doses and including CBD in their regimens. Quite simply, my patients are using cannabis as medicine, responsibly and thoughtfully.

I ask every patient if they have any side effects and the majority report that they have none. Any side effects that patients experience can often be resolved with changes in delivery method, CBD:THC ratios, chemovars or dosing.

However, studies have shown medical risks from cannabis in certain situations. These include possible increased risks to those with cardiovascular disease, pulmonary risks from smoking, risks from accidental injury while under the influence of cannabis, risks during pregnancy and breastfeeding, and risks in the pediatric population, specifically to developing brains.

It is important to understand that the studies noted here focused primarily on those using THC-rich cannabis, and that the findings listed in this chapter do not apply to CBD-rich cannabis.

Cardiovascular Risks associated with THC use

What we know about THC and its effects on the heart and blood pressure:

• THC causes an increase in heart rate within minutes of use; heart rate will return to normal after a few hours; the heart rate increases by about 20-50 beats per minute.
• THC can cause an elevation of blood pressure when one is lying flat but there is a risk of blood pressure dropping if one stands too quickly.
• Many sources cite that blood pressure decreases due to vasodilation of the blood vessels and overall relaxation with THC use.
• The cardiovascular effects of THC are more pronounced in the new or inexperienced user; regular users of THC develop a tolerance to these effects; tolerance to THC itself is not dangerous but can eventually decrease the effectiveness of the medicinal benefits.

Summary of scientific studies:

• Three studies showed a rare association with possible development of abnormal cardiac rhythms with THC use.^1,2,3
• In one study, smoking THC-rich cannabis was related to a more rapid onset of chest pain in patients with a history of chest pain when they underwent a stress test shortly after smoking a marijuana cigarette. It’s noted that this effect may be due to the carbon monoxide in the smoke as opposed to a THC effect.⁴
• One study showed an increased relative risk of developing a heart attack in the first hour after smoking marijuana (4.8 times increased risk over baseline).⁵
• There are a few case reports of young persons who have had heart attacks, arrhythmias and even cardiac arrest after using cannabis.^6,7 Note that there are only a few case reports in scientific literature and other factors such as tobacco use, alcohol use and previously unknown cardiac disease may have played a role.
• One study showed marijuana use was associated with three-fold greater mortality following acute myocardial infarction, with a graded increase in risk with more frequent use.⁸
• A recent review of the risk of cardiovascular disease (this definition included coronary artery disease, heart attack, heart failure, cardiac chest pain, and stroke) in 3,051 people revealed that marijuana use was not significantly associated with an increased risk of cardiovascular disease.⁹

It appears that there is a risk, however rare, of myocardial infarction, arrhythmias and even cardiac arrest with cannabis use. Remember that the above findings relate to THC use, not CBD use. The best approach in these situations is for those patients with known cardiovascular disease who are investigating the use of medical cannabis to discuss the scientific data available, the risks and the benefits with their personal physician, cardiologist and a knowledgeable cannabis specialist. If the decision to use medical cannabis is made, these patients should avoid smoking by choosing a different method of delivery, such as edibles or tinctures, and they should consider using CBD-rich cannabis products.

Pulmonary Risks of Smoking Cannabis

What we know about cannabis smoke:

• Cannabis smoke contains similar contents to tobacco smoke, including ammonia, hydrocyanic acid, nitrosamines, and tar components including phenols and naphthalene. Carcinogenic compounds including benzopyrene and benzanthracene are also in cannabis smoke.
• Very importantly, cannabis smoke does not contain nicotine and does contain phytocannabinoid compounds.
• Tobacco smoke causes narrowing of the airways but cannabis smoke causes bronchodilation, opening of the airways. THC has been found to be the compound causing this effect with cannabis smoke.

Summary of scientific studies:

• Smokers of tobacco only, cannabis only and smokers of both have increased incidence of respiratory symptoms, including chronic cough, phlegm production, wheezing and bronchitis when compared to non-smokers.^10,11
• Multiple studies document that chronic cannabis smoking (without tobacco use) is associated with an increased prevalence of bronchitis.^{12,13,14,15,16}
• Symptoms of chronic bronchitis from smoking cannabis alone resolve with cessation of smoking.¹⁷
• Studies on lung function in chronic cannabis smokers are conflicting, with some studies showing no difference from non-smokers, others showing mild airflow obstruction.^18,19,20
• Two large studies failed to show an association between cannabis smoking and lung cancer.^21,22
• A large study comparing 611 lung cancer cases, 601 upper airway cancer cases and 1,040 matched control subjects found no associations between cannabis use and risk of cancer; however, the study reports that the risk of cancer was clearly associated with tobacco use.²³
• A study investigating the combined effects of tobacco and cannabis smoking revealed that smoking both tobacco and marijuana synergistically increased the risk of respiratory symptoms and COPD (chronic obstructive pulmonary disease, also called emphysema) but that smoking only marijuana was not associated with an increased risk of respiratory symptoms or COPD.²⁴

In summary, it appears that chronic smokers, whether using tobacco or cannabis, have an increased risk of developing respiratory symptoms such as chronic cough, bronchitis, wheezing and increased phlegm. Studies do not show an increased risk of cancer with cannabis smoke despite the presence of carcinogenic compounds. It has been hypothesized that the presence of cannabinoid compounds in cannabis smoke may be protective against the development of cancer but definitive research remains to be done.

To quote Dr. Donald Tashkin, a pulmonologist at UCLA and the world’s leading researcher of the effects of cannabis smoke on the lungs, “the risks of pulmonary complications of regular use of marijuana appear to be relatively small and far lower than those of tobacco smoking. However, such potential pulmonary risks need to be weighed against possible benefits in consideration regarding medicinal use of marijuana.”²⁵

Since there are many different methods available to patients who want to use cannabis medicine, one does not have to smoke it in order to reap the benefits. In a survey of my patients, approximately 80% who switched from smoking to vaporization found excellent results and no longer smoked. Those who continue to smoke often obtain cannabis flower that is higher in potency so they can smoke less to achieve the same effect. Since sublingual and edible preparations are now regularly tested and properly labeled, they are more reliable than they have been in the past, and many patients can achieve the same medicinal benefit without smoking.

Risks of Accidental Injury with THC use

Summary of scientific studies:

• Driving simulator studies show that cannabis can adversely affect certain driving skills, in particular tracking ability, attentiveness, judgment of speed and distance, peripheral vision and coordination at complex tasks.^26,27
• A comprehensive survey of 10 years of U.S. accident data found that alcohol-free drivers with THC in their system had a slightly elevated risk of unsafe driving behavior, but lower than that for drivers with legal amounts of alcohol in their blood.²⁸
• Studies have found that THC is significantly more hazardous in the first one-two hours of acute intoxication.^29,30
• Alcohol and THC used together increases the risk of fatal accidents.³¹
• A number of studies showed the odds of causing death or injury were slightly lower in cannabis users than in people who had not used drugs.^32,33,34,35
• It is postulated that drivers under the influence of cannabis may have lower risks of motor vehicle accidents because of “over-compensation behavior,” that is, they appear to drive slower and avoid adverse driving situations.³⁶

Although the studies may be conflicting, a few things are clear. Driving while under the influence of any psychoactive drug is a bad idea. Combining cannabis with alcohol is dangerous and increases the risk of accidents. Although cannabis patients may over-compensate while driving under the influence and actually be less at risk, it is illegal to drive under the influence, and this is not advised in any circumstance.

Pregnancy and Breastfeeding with THC use

Summary of scientific studies:

• It has been reported that THC crosses the placenta and enters the circulation of the fetus, reaching concentration of 10% – 30% of the maternal concentration.³⁷
• One study suggests prenatal cannabis use resulted in a decrease in fetal growth, while another study reports an increase in fetal growth, although neither controlled for socioeconomic status or use of other substances.^38,39
• An increased incidence of preterm labor has been reported while other studies fail to find any association between preterm labor and maternal cannabis use.⁴⁰
• A recent study found maternal cannabis use specifically was associated with a small increase of risk for aggressive behavior and attention problems in 18-month-old girls, but not boys.⁴¹
• Slightly reduced motor development in 1 year olds whose mothers reported smoking cannabis during breastfeeding has been reported, but no effect on mental development was noted.⁴²
• In another study of 27 infants evaluated at 1 year of age who were exposed to marijuana via breast milk (compared to 35 non exposed infants), no significant differences were found in terms of age at weaning, growth, and mental or motor development.⁴³
• No significant physical or psychological differences were found between three-day old newborns of heavy marijuana-using mothers and non-users in Jamaica.⁴⁴
• A recent comprehensive review of all studies concluded that there is a subtle association between prenatal cannabis exposure and certain neurobehavioral and cognitive deficits, and these findings appear to be primarily associated with children exposed to heavy amounts of cannabis as well as alcohol and/or tobacco.⁴⁵

As you can see, studies on maternal cannabis use during pregnancy and breastfeeding reveal conflicting results. Although it appears to be safe overall, most physicians do not recommend drug use of any kind during pregnancy or breastfeeding unless there are special circumstances such as severe morning sickness or other serious symptoms that cannot be safely treated with other medications.

By far, the largest risk I have seen as a cannabis physician is the risk of having a newborn taken away by Child Protective Services if either the mother or the newborn has a positive THC drug test during the pregnancy or at the time of birth. Cannabis use still remains controversial in general and use by pregnant women is especially frowned upon by society and the medical community.

I have been involved in a number of cases where the mother or infant tested positive for THC and the aggressiveness of social workers and the legal system is astounding, especially when the scientific literature is inconclusive. Tobacco smoking and use of alcohol during pregnancy both have significant proven risks, such as fetal alcohol syndrome, increased risk of premature birth, etc., and are not targeted by our legal system. Until society, the medical community, and legal system have an understanding of the true risks of cannabis use during pregnancy, I advise women who are pregnant not to use cannabis to avoid the devastation of having their baby removed from the family by Child Protective Services.

Risks of THC use in Pediatric Population

Human brain development and the role of the endocannabinoid system throughout childhood and adolescence has been the focus of a number of scientific studies. The adolescent brain is different from the mature adult brain in its structure and in the way it’s neurotransmitters function. There is an increased sensitivity to changes and exposures in its environment, resulting in a vulnerability of the adolescent brain that is not present once the brain fully develops.

Researchers have found that endocannabinoids are crucial in influencing how neurotransmitters in the developing brain promote proper circuitry and new brain growth. The endocannabinoid system goes through necessary changes during the adolescent years, with heightened cannabinoid receptor density and possibly sensitivity. Interference with these changes, for example the use of THC, which can over-activate the cannabinoid receptor, may interfere with the development of the mature brain.^{46,47 Normal endocannabinoid system functioning during these critical years is required for emotional and cognitive functions to develop and mature correctly.48}

One researcher summed up the importance of the endocannabinoid system in the developing brain this way, “endocannabinoid signaling is an important determinant of maturation of the adult brain … it seems quite likely that disruption of normative endocannabinoid signaling during adolescence may have long-standing consequences on adult brain function.”⁴⁹

Summary of scientific studies:

• Numerous animal studies have documented that THC or synthetic cannabinoids given to adolescent animals induce changes in emotional behavior, reward response, endocannabinoid levels, and impulsivity.^50,51,52
• Studies in human adolescents (ages 12-18 years) who are heavy users of THC-rich cannabis have shown that the interference of the normal endocannabinoid system functioning may result in some long-lasting brain changes that may be deleterious, especially in the areas of emotional and mental illness (especially anxiety disorders), impulsivity control, memory issues, attention, decision-making and lowered overall and verbal IQ. First time cannabis use after the age of 18 years was not associated with lowered IQ or neurocognitive performance.^53,54
• Although schizophrenia does not develop in the majority of teenagers that use cannabis, those with increased risk factors, such as schizophrenia or mental illness in a family member and chronic heavy cannabis use at a young age, have an increased risk of developing schizophrenia as a young adult.^55,56,57

As a pediatrician, medical cannabis specialist and the mother of a teenager, I am strongly opposed to healthy or otherwise “typically” developing children and adolescents using cannabis. I am also opposed to cannabis use (and pharmaceutical use) in children and adolescents with mild illnesses, such as occasional anxiety or sleep disturbance, as other treatment modalities (talk therapy, exercise, proper diet, sleep hygiene, etc.) can and should be used in these instances. However, children and adolescents with moderate to severe medical conditions that either significantly disrupt quality of life or are life-threatening or life-limiting should absolutely have the option of using cannabis under medical supervision.