Preliminary studies have shown chronic lung disease in some marijuana users. There are more known cancer-causing agents in marijuana smoke than in cigarette smoke. Even small doses of marijuana can impair memory function, distort perception, hamper judgment, and diminish motor skills. Health effects also include accelerated heartbeat and, in some persons, increased blood pressure. These changes pose health risks for anyone, but particularly for people with abnormal heart and circulatory conditions, such as high blood pressure and hardening of the arteries.
Mood changes occur with the first use.
Observers in clinical settings have noted increased apathy, loss of ambition, loss of effectiveness, diminished ability to carryout long-term plans, difficulty in concentrating, and a decline in school or work performance. Many teenagers who end up in drug treatment programs started using marijuana at an early age. Driving under the influence of marijuana is especially dangerous. Marijuana impairs driving skills for at least 4 to 6 hours after smoking a single cigarette. When marijuana is used in combination with alcohol, driving skills become even more impaired.