Adverse Effects of Marijuana (for the general public)

Proposition 19, The Regulate, Control and Tax Cannabis Act of 2010 that would legalize all use of marijuana for Californians 21 years and older, not only falsely claims that “cannabis is not physically addictive,” but also states that marijuana “does not have long term toxic effects on the body” In fact, marijuana does often have serious toxic effects on the brain and body.

All drugs and medicines have a “side effect profile” – unintended negative symptoms – that accompany the desired purpose for which the drug is taken. Whether marijuana is considered a recreational drug or a medicine, it has a powerful impact on the brain and the rest of the body that sometimes leads to impairments and illness. Chronic and heavy use increases the possibility that these “side effects” take a significant toll on one’s health.

The following information briefly summarizes the health consequences of marijuana that have been documented by research studies. For further details and references, please refer to the section for “Healthcare Professionals.”

The adverse effects on health caused by smoking marijuana can be divided into the following broad categories:

Brain Function


  • Marijuana intoxication causes well defined impairments in the following brain functions: Memory, sense of time, sensory perception, attention span, problem solving, verbal fluency, reaction time, and psychomotor control.
  • The short-term effects of marijuana last approximately 1-4 hours, depending on potency of the marijuana, the route of administration, and the tolerance of the user.
  • Marijuana intoxication impairs intellectual activities as well as activities that require bodily control, such as driving.


  • Heavy marijuana use can cause lasting subtle, but persisting, impairments in brain function that impact memory, attention, learning, and information processing.
  • Compared to adults, children and adolescents have a much greater vulnerability to the toxic effects of marijuana on the brain, especially when alcohol and marijuana are used together.

Psycho-Social Health

Mental Health

  • Heavy use of marijuana can lead to addiction.
  • Marijuana can cause psychosis, a state of mind characterized by an inability to distinguish between what is real and what is not.
  • Marijuana increases the risk of developing schizophrenia.
  • Marijuana has been strongly associated with panic, anxiety and depressive disorders.

Social Function

  • Marijuana use is strongly associated with poor school performance.
  • Among adolescents with pre-existing educational difficulties, marijuana use may lead to school failure, an event with lifelong consequences on occupational opportunities.
  • Among adults, marijuana is associated with lower occupational status and higher unemployment.

Physical Health

Health Effects

  • Marijuana smoke contains much of the same tar and chemicals found in tobacco smoke, leading to the inflammation of bronchitis.
  • Marijuana harms cells lining the respiratory tract, leading to pre-cancerous changes associated with lung cancer, as well as head and neck cancer.
  • Marijuana stimulates the heart rate and blood pressure, which increases the risk of heart attack among individuals with pre-existing heart disease.

Reproductive Effects

  • The compounds found in marijuana readily cross the placenta, where the growing fetus absorbs them, and pass into breast milk, where the nursing infant ingests them.
  • Marijuana use during pregnancy and early development has been linked to low birth weight, developmental delay, and behavioral problems including addiction.
  • Marijuana affects many aspects of reproductive physiology in both men and women, though the long-term consequences of these effects remain unclear.