What are marijuana’s effects on general physical health?
Within a few minutes after inhaling marijuana smoke, a person's heart rate speeds up, the breathing passages relax and become enlarged, and blood vessels in the eyes expand, making the eyes look bloodshot (red). The heart rate—normally 70 to 80 beats per minute—may increase by 20 to 50 beats per minute or may even double in some cases. Taking other drugs with marijuana can amplify this effect.
Limited evidence suggests that a person's risk of heart attack during the first hour after smoking marijuana is nearly five times his or her usual risk.67 This observation could be partly explained by marijuana raising blood pressure (in some cases) and heart rate and reducing the blood’s capacity to carry oxygen.68 Marijuana may also cause orthostatic hypotension (head rush or dizziness on standing up), possibly raising danger from fainting and falls. Tolerance to some cardiovascular effects often develops with repeated exposure.69 These health effects need to be examined more closely, particularly given the increasing use of "medical marijuana" by people with health issues and older adults who may have increased baseline vulnerability due to age-related cardiovascular risk factors (see "Marijuana as Medicine," below).
Marijuana smoke, like tobacco smoke, is an irritant to the throat and lungs and can cause a heavy cough during use. It also contains toxic gases and particles that can damage the lungs. Marijuana smoking is associated with large airway inflammation, increased airway resistance, and lung hyperinflation, and regular marijuana smokers report more symptoms of chronic bronchitis than non-smokers.70 Smoking marijuana may also reduce the respiratory system’s immune response, increasing the likelihood of the user acquiring respiratory infections, including pneumonia.71 One study found that frequent marijuana smokers used more sick days than other people, often because of respiratory illnesses.72
Marijuana as Medicine
The potential medicinal properties of marijuana and its components have been the subject of research and heated debate for decades. THC itself has proven medical benefits in particular formulations. There are two FDA-approved, THC-based medications, dronabinol (Marinol®) and nabilone (Cesamet®), prescribed in pill form for the treatment of nausea in patients undergoing cancer chemotherapy and to stimulate appetite in patients with wasting syndrome due to AIDS.
In addition, several other marijuana-based medications have been approved or are undergoing clinical trials. Nabiximols (Sativex®), a mouth spray that is currently available in the United Kingdom, Canada, and several European countries for treating the spasticity and neuropathic pain that may accompany multiple sclerosis, combines THC with another chemical found in marijuana called cannabidiol (CBD). CBD does not have the rewarding properties of THC, and anecdotal reports indicate it may have promise for the treatment of seizure disorders, among other conditions. A CBD-based liquid medication called Epidiolex is currently being tested in the United States for the treatment of two forms of severe childhood epilepsy, Dravet syndrome and Lennox-Gastaut syndrome.
Medications like these, which use purified chemicals derived from or based on those in the marijuana plant, are generally considered by researchers to be more promising therapeutically than use of the whole marijuana plant or its crude extracts. Development of drugs from botanicals such as the marijuana plant poses numerous challenges. Botanicals may contain hundreds of unknown, active chemicals, and it can be difficult to develop a product with accurate and consistent doses of these chemicals. Use of marijuana as medicine also poses other problems such as the adverse health effects of smoking and THC-induced cognitive impairment. Nevertheless, a growing number of states have legalized dispensing of marijuana or its extracts to people with a range of medical conditions.
An additional concern with "medical marijuana" is that little is known about the long-term impact of marijuana use by people with health- and/or age-related vulnerabilities to whom it is dispensed—such as older adults or people with cancer, AIDS, cardiovascular disease, multiple sclerosis, or other neurodegenerative diseases. Further research will be needed to determine whether people whose health has been compromised by disease or its treatment (e.g., chemotherapy) are at greater risk for adverse health outcomes from marijuana use.
Whether smoking marijuana causes lung cancer, as cigarette smoking does, is less certain. Although marijuana smoke contains carcinogenic (cancer-causing) combustion products, evidence for a link between marijuana use and lung cancer has thus far been inconclusive.73 The very different ways marijuana and tobacco are used, including factors like how frequently they are smoked during the day and how long the smoke is held in the lungs, as well as the fact that many people use both substances make determining marijuana’s precise contribution to lung cancer risk, if any, difficult to establish. This is an area that will require more research.
However, a few studies have shown a clear link between marijuana use in adolescence and increased risk for an aggressive form of testicular cancer (non-seminomatous testicular germ cell tumor) that predominantly strikes young adult males.74,75 The early onset of testicular cancers compared to lung and most other cancers indicates that, whatever the nature of marijuana’s contribution, it may accumulate over just a few years of use.
This series of reports simplifies the science of research findings for the educated lay public, legislators, educational groups, and practitioners. The series reports on research findings of national interest.