Short-term Acute negative effects may include anxiety and panic, impaired attention and memory, an increased risk of psychotic symptoms, the inability to think clearly, and an increased risk of accidents. Cannabis impairs a person's driving ability, and THC was the illicit drug most frequently found in the blood of drivers who have been involved in
vehicle crashes. Those with THC in their system are from three to seven times more likely to be the cause of vehicle crash than those who had not used either cannabis or alcohol. Some immediate undesired side effects include a decrease in short-term memory, dry mouth, impaired motor skills, reddening of the eyes, dizziness, feeling tired and vomiting.
Fatality A systematic meta analysis showed that cannabis users double the chance of dying from heart disease. Cannabis users had a 29% higher risk of heart attack and a 20% higher risk of stroke than non-users. There is an association between cannabis use and suicide, particularly in younger users. A 16-month survey of Oregon and Alaska emergency departments found a report of the death of an adult who had been admitted for acute cannabis toxicity. A recent study in 2025 suggests that individuals diagnosed with cannabis use disorder—characterized by an inability to stop using cannabis despite its negative effects—face a nearly threefold increase in
mortality rates compared to those without the condition over a five-year period. The research indicates that people with this disorder are ten times more likely to die by suicide than the general population. Additionally, they have a higher risk of death from trauma, drug poisoning, and lung cancer. In a separate study researchers found an increase in
schizophrenia and
psychosis cases in
Canada linked to cannabis use disorder following the drug's legalization.
Long-term regarding 20 popular recreational drugs. Cannabis was ranked 11th in dependence, 17th in physical harm, and 10th in social harm.
Psychological effects A 2015 meta-analysis found that, although a longer period of abstinence was associated with smaller magnitudes of impairment, both retrospective and
prospective memory were impaired in cannabis users. The authors concluded that some, but not all, of the deficits associated with cannabis use were reversible. A 2012 meta-analysis found that deficits in most domains of cognition persisted beyond the acute period of intoxication, but was not evident in studies where subjects were abstinent for more than 25 days. Few high quality studies have been performed on the long-term effects of cannabis on cognition, and the results were generally inconsistent. Furthermore,
effect sizes of significant findings were generally small. Impairments in executive functioning are most consistently found in older populations, which may reflect heavier cannabis exposure, or developmental effects associated with adolescent cannabis use. One review found three prospective cohort studies that examined the relationship between self-reported cannabis use and
intelligence quotient (IQ). The study following the largest number of heavy cannabis users reported that IQ declined between ages 7–13 and age 38. Poorer school performance and increased incidence of leaving school early were both associated with cannabis use, although a causal relationship was not established. Cannabis users demonstrated increased activity in task-related brain regions, consistent with reduced processing efficiency. A reduced
quality of life is associated with heavy cannabis use, although the relationship is inconsistent and weaker than for tobacco and other substances. The direction of
cause and effect, however, is unclear. reduced
hippocampal volume is consistently found.
Amygdala abnormalities are sometimes reported, although findings are inconsistent. There is evidence that amygdala volume is smaller in cannabis users. Cannabis use is associated with increased recruitment of task-related areas, such as the
dorsolateral prefrontal cortex, which is thought to reflect compensatory activity due to reduced processing efficiency. Cannabis use is also associated with downregulation of
CB1 receptors. The magnitude of down regulation is associated with cumulative cannabis exposure, and is reversed after one month of abstinence. There is limited evidence that chronic cannabis use can reduce levels of
glutamate metabolites in the human brain.
Cannabis dependence About 9% of those who experiment with marijuana eventually become dependent according to
DSM-IV (1994) criteria. Of daily users, about 50% experience withdrawal upon cessation of use (i.e. are dependent), characterized by sleep problems, irritability, dysphoria, and craving. According to
DSM-5 criteria, 9% of those who are exposed to cannabis develop cannabis use disorder, compared to 20% for
cocaine, 23% for
alcohol and 68% for
nicotine. Cannabis use disorder in the DSM-5 involves a combination of DSM-IV criteria for cannabis abuse and dependence, plus the addition of craving, without the criterion related to legal troubles. At an epidemiological level, a
dose–response relationship exists between cannabis use and increased risk of
psychosis and earlier onset of psychosis. Although the epidemiological association is robust, evidence to prove a causal relationship is lacking. Cannabis may also increase the risk of depression, but insufficient research has been performed to draw a conclusion. Cannabis use is associated with increased risk of anxiety disorders, although causality has not been established. A 2025 systematic review and meta-analysis involving more than half a million participants aged 15–30 reported that cannabis use was associated with higher odds of depression (51% higher), anxiety (58%), suicidal ideation (65%), and suicide attempt (87%). A review in 2019 found that research was insufficient to determine the safety and efficacy of using cannabis to treat schizophrenia, psychosis, or other
mental disorders. Another found that cannabis during adolescence was associated with an increased risk of developing depression and suicidal behavior later in life, while finding no effect on anxiety.
Physical Heavy, long-term exposure to marijuana may have physical, mental, behavioral and social health consequences. It may be "associated with diseases of the liver (particularly with co-existing
hepatitis C), lungs, heart, and vasculature". A 2014 review found that while cannabis use may be less harmful than alcohol use, the recommendation to substitute it for
problematic drinking was premature without further study. Various surveys conducted between 2015 and 2019 found that many users of cannabis substitute it for
prescription drugs (including opioids), alcohol, and tobacco; most of those who used it in place of alcohol or tobacco either reduced or stopped their intake of the latter substances.
Cannabinoid hyperemesis syndrome (CHS) is a severe condition seen in some chronic cannabis users where they have repeated bouts of uncontrollable vomiting for 24–48 hours. Four cases of death have been reported as a result of CHS. A limited number of studies have examined the
effects of cannabis smoking on the respiratory system. Chronic heavy marijuana smoking is associated with
respiratory infections, coughing, production of sputum, wheezing, and other symptoms of chronic bronchitis. Short-term use of cannabis is associated with
bronchodilation. Other side effects of cannabis use include
cannabinoid hyperemesis syndrome (CHS), a condition which involves recurrent nausea, cramping abdominal pain, and vomiting. A 2025 systematic review and meta-analysis of eight observational studies, including more than 160,000 participants, found that cannabis users had significantly greater odds of having
asthma compared with non-users (pooled odds ratio = 1.31; 95% confidence interval 1.19–1.44). Subgroup analyses showed similar associations across both cross-sectional and cohort studies, and a
dose-dependent trend was noted in several datasets. The authors concluded that cannabis use, particularly by inhalation, may increase the risk of asthma and recommended monitoring respiratory health among cannabis users. Cannabis smoke contains thousands of organic and inorganic chemical compounds. This
tar is chemically similar to that found in tobacco smoke, and over fifty known
carcinogens have been identified in cannabis smoke, including; nitrosamines, reactive aldehydes, and
polycyclic aromatic hydrocarbons, including benz[a]pyrene. Cannabis smoke is also inhaled more deeply than tobacco smoke. , there is no consensus regarding whether cannabis smoking is associated with an increased risk of cancer. Light and moderate use of cannabis is not believed to increase risk of lung or upper airway cancer. Evidence for causing these cancers is mixed concerning heavy, long-term use. In general there are far lower risks of pulmonary complications for regular cannabis smokers when compared with those of tobacco. A 2015 review found an association between cannabis use and the development of testicular
germ cell tumors (TGCTs), particularly non-
seminoma TGCTs. Another 2015 meta-analysis found no association between lifetime cannabis use and risk of head or neck cancer. Combustion products are not present when using a
vaporizer, consuming THC in pill form, or consuming
cannabis foods. There is concern that cannabis may contribute to cardiovascular disease, but , evidence of this relationship was unclear. Research in these events is complicated because cannabis is often used in conjunction with tobacco, and drugs such as alcohol and cocaine that are known to have cardiovascular risk factors. Smoking cannabis has also been shown to increase the risk of
myocardial infarction by 4.8 times for the 60 minutes after consumption. There is preliminary evidence that cannabis interferes with the
anticoagulant properties of prescription drugs used for
treating blood clots. , the mechanisms for the
anti-inflammatory and possible
pain relieving effects of cannabis were not defined, and there were no governmental regulatory approvals or clinical practices for use of cannabis as a drug. At one Colorado medical center following legalization, approximately two percent of ER admissions were classified as cannabis users. The symptoms of one quarter of these users were partially attributed to cannabis (a total of 2567 out of 449,031 patients); other drugs were sometimes involved. Of these cannabis admissions, one quarter were for
acute psychiatric effects, primarily
suicidal ideation, depression, and anxiety. An additional third of the cases were for gastrointestinal issues including
cannabinoid hyperemesis syndrome. According to the United States Department of Health and Human Services, there were 455,000 emergency room visits associated with cannabis use in 2011. These statistics include visits in which the patient was treated for a condition induced by or related to recent cannabis use. The drug use must be "implicated" in the emergency department visit, but does not need to be the direct cause of the visit. Most of the illicit drug emergency room visits involved multiple drugs. In 129,000 cases, cannabis was the only implicated drug.
Reproductive health Secondhand cannabis smoke A 2022 study found that smoking cannabis using a bong can greatly increase background levels of
fine particulate matter, a
carcinogen, in an enclosed space such as a living room. After 15 minutes, mean levels of particulate matter were more than twice the
Environmental Protection Agency hazardous air quality threshold, and after 140 minutes, the concentrations were four times greater than those generated by smoking tobacco using a cigarette or hookah. This suggests secondhand cannabis smoke from bongs may present a health risk to non-smokers. ==Pharmacology==