Research has shown that infants exposed to marijuana in uterus display altered responses to visual stimuli and increased tremulousness, which may indicate problems with neurological development. Other studies have shown that during infancy and preschool years, marijuana-exposed children have more behavioral problems than non-exposed children. Research also shows that marijuana-exposed children perform visual perception, sustained attention, language comprehension, and memory tasks more poorly when compared with unexposed children.

Acute (present during intoxication)

• Impairs short-term memory.
• Impairs attention, judgment, and other cognitive functions.
• Impairs coordination, balance, and reaction time.
• Increases heart rate.

Persistent (lasting longer than intoxication, but may not be permanent)

• Impairs memory.
• Impairs learning skills.
• Increases risk of chronic cough, bronchitis, and emphysema.
• Long-term (cumulative, potentially permanent effects of chronic abuse)
• Can lead to addiction.
• Increases risk of cancer of the head, neck, and lungs.

Because marijuana contains irritants and carcinogens, it promotes cancer of the lungs and other parts of the respiratory tract. Marijuana also produces high levels of an enzyme that converts some hydrocarbons into their carcinogenic form. These levels may accelerate the changes that ultimately produce malignant cells. Additionally, marijuana users typically inhale more deeply and hold their breath longer than tobacco smokers, increasing the lungs exposure to carcinogenic smoke.

Users who smoke marijuana regularly may experience the same respiratory problems as tobacco smokers, including daily cough and phlegm, symptoms of chronic bronchitis, and frequent chest colds. Continued marijuana use can result in abnormal functioning of lung tissue injured or destroyed by marijuana smoke.

Within a few minutes after smoking marijuana, the user's heart begins to beat more rapidly and may increase by 20 to 50 beats per minute or double. Results of a study released in 2001 indicate that a person's risk of heart attack within the 1st hour of smoking marijuana is four times the usual risk.