Side Effects & Safety
When taken by mouth: Cannabis is POSSIBLY UNSAFE when taken by mouth in large amounts or for a long time. Cannabis containing large amounts of THC (50 mg or more) has been linked with anxiety, psychosis, heart attack, and irregular heart rhythm. Regularly taking large amounts of cannabis over a long period of time might cause a disorder called cannabinoid hyperemesis syndrome, or CHS. CHS leads to severe, repeated bouts of nausea and vomiting that don’t respond to typical anti-nausea medicine. In a few reports, CHS has been linked to severe complications that caused death.
Using cannabis for at least 1-2 weeks can also lead to dependence. People with cannabis dependence might experience withdrawal after stopping cannabis use. Symptoms of withdrawal include nervousness, shaking, trouble sleeping, decreased appetite, sweating, headache, and depressed mood. There isn’t enough information to know if cannabis is safe to use in moderation for short periods of time.
When sprayed into the mouth: A specific cannabis extract spray (Sativex, GW Pharmaceuticals) is POSSIBLY SAFE when applied under the tongue. Side effects may include headache, dizziness, drowsiness, dry mouth, nausea, and paranoid thinking. This cannabis extract spray is available as a prescription-only product in the U.K. and Canada. It has not been approved as a prescription product in the U.S.
When inhaled: Cannabis is POSSIBLY UNSAFE when inhaled. Smoking or vaping cannabis can cause various breathing problems such as wheezing and coughing. Some reports suggest that smoking cannabis might cause air-filled cavities in the lungs. These air-filled cavities can cause symptoms such as chest pressure, soreness, and difficulty breathing. Use of e-cigarettes and other vaping products containing THC has been linked to serious lung injury in some people. Smoking cannabis can also cause headache, dizziness, drowsiness, dry mouth, nausea, and paranoid thinking. Smoking cannabis might also increase appetite, increase heart rate, change blood pressure, and impair mental functioning. Some reports suggest that smoking cannabis may also increase the risk of heart problems such as heart attack and abnormal heart rhythm. Regularly smoking large amounts of cannabis for a long time may cause CHS. It might also lead to dependence. People with cannabis dependence might experience withdrawal after stopping cannabis use. Symptoms of withdrawal include nervousness, shaking, trouble sleeping, decreased appetite, sweating, headache, and depressed mood.
Special Precautions & Warnings:
Pregnancy: Cannabis is UNSAFE when taken by mouth or smoked during pregnancy. Cannabis passes through the placenta and can slow the growth of the fetus and increase the risk for premature birth. Cannabis use during pregnancy is also associated with stillbirth, childhood leukemia, abnormalities in the fetus, and the need for intensive care after birth. Cannabis use during pregnancy has also been linked with lower intelligence and increased emotional problems in children when they grow up. Also, cannabis use is associated with an increased risk for anemia and high blood pressure in the mother.
Breast-feeding: Using cannabis, either by mouth or by inhalation is LIKELY UNSAFE during breast-feeding. The chemicals in cannabis pass into breast milk. Too much of these chemicals might slow down the development of the baby.
Bipolar disorder: Using cannabis might make manic symptoms worse in people with bipolar disorder.
Heart disease: Cannabis might cause fast heartbeat and high blood pressure. It might also increase the risk of a having heart attack. However, in many cases, people who experienced these events after smoking cannabis had other risk factors for heart-related events such as smoking cigarettes or being overweight.
A weakened immune system: Certain chemicals in cannabis can weaken the immune system. This might make it more difficult for the body to fight infections.
Allergies to fruits and vegetables: Cannabis might increase the risk of an allergic reaction in people with allergies to foods like tomatoes, bananas, and citrus fruit.
Depression: Cannabis use, especially frequent use, might increase the chance of getting depression. It can also worsen symptoms of depression and increase thoughts about suicide in those that already have depression.
Diabetes: Cannabis use might make it harder to control blood sugar levels. It might also increase the risk for long-term complications from diabetes. Until more is known, be cautious using cannabis.
Liver disease: It is unclear if cannabis worsens chronic liver disease. While some weak evidence suggests that there might be a link, other evidence has not found a link. Until more is known, be cautious using cannabis.
Multiple sclerosis: Taking cannabis by mouth might make symptoms of multiple sclerosis worse.
Lung diseases: Cannabis can make lung problems worse. Regular use over a period of years might increase the risk of lung cancer. Some people develop a type of lung disease called emphysema.
Schizophrenia: Using cannabis might make symptoms of schizophrenia worse.
Quitting smoking: Using cannabis might make it harder to quit smoking. Early research suggests that people who use cannabis and want to quit smoking cigarettes are less likely to quit smoking after 6 months than people who don’t use cannabis.
Stroke: Using cannabis after having a stroke might increase the risk of having a second stroke.
Surgery: Cannabis affects the central nervous system or the brain and nerves. It might slow the central nervous system too much when combined with anesthesia and other medications during and after surgery. Stop using cannabis at least 2 weeks before a scheduled surgery.