Marijuana is legal in two U.S. states, so it must be safe, right? That may be the message teens are hearing. A survey from the National Institute on Drug Abuse finds the use of pot is up among high school students while the perceived risk of smoking it is down. Researchers worry this could lead to a greater increase in its use in the future. Meanwhile, a Dutch study says marijuana use may be linked to psychotic symptoms later in life. Reuters Health wrote about the study and medwireNews covered the survey.

By Mary Pickett, MD
Harvard Medical School

What Is the Doctor's Reaction?

Marijuana is now legal in two states. Teenagers are using the drug more, believing it to be safe. At one U.S. school this week, teens got in trouble for selling marijuana-laced brownies at a bake sale. According to a survey of nearly 45,000 teens from 395 U.S. high schools, one third of 12th graders have used marijuana in 2012. One out of five used the drug in the month of the survey. The National Institute on Drug Abuse published these survey results last week. I am seeing more marijuana use among my adult patients, as well.

But is marijuana safe? No.

There are risks from marijuana. A Dutch study this week confirmed that marijuana use can cause damage to the brain, resulting in psychotic symptoms (with or without a diagnosis of schizophrenia) later in life. A nearly doubled risk for psychosis had been seen among marijuana users in studies from 2004 and 2010, but it was hard to know from these studies if marijuana led to psychosis or if psychosis led people to use marijuana more often. This week's study confirms that some of the increased risk is an effect of marijuana and not just a coincidence.

Regular marijuana users are more likely to be diagnosed with schizophrenia later in adulthood. Schizophrenia causes recurring episodes of psychosis. Full-blown schizophrenia has complicated origins, involving an inherited predisposition.

Psychotic symptoms occur when you are not dreaming, not half-asleep and not under the influence of drugs or alcohol.

Here are examples of psychotic symptoms:

Hallucination symptoms:

• Seeing a vision other people cannot see
• Hearing voices other people do not hear, such as a voice from inside your head or a voice out of the air when no one is speaking around you

Experiences of mind control or magic:

• Believing thoughts in your mind are controlled by someone else or by another force. For example, you might believe thoughts were inserted into your head.
• Believing your behaviors are controlled by an outside force and they are making you do things you do not choose to do
• Believing you receive special or magical communication through the radio, television or other media

Paranoid delusions:

• Being convinced there is a plot to harm you or that people are following you, when friends or family do not believe this is true

What Changes Can I Make Now?

Understand the risks of marijuana. It is not a safe drug. It is habit forming and hazardous.

• Lung disease
  Smoking three or four marijuana cigarettes per day has the same lung disease risk as smoking 20 nicotine cigarettes.
• Cancers
  Marijuana can cause cancer in the head and neck and increases lung cancer risk.
• Heart attack
  Risk is higher immediately after you smoke marijuana.
• Infertility and lower sex drive
  In men, marijuana affects the function and quantity of sperm, reduces testosterone levels and sexual drive, enlarges male breasts and causes impotence. In women, period cycles can become shorter and fertility can be reduced. It can cause spontaneous leakage of milk from the breasts.
• Effects in pregnancy
  Marijuana reduces the birth weight of babies.
• Psychiatric effects
  Marijuana increases the risk for depression, schizophrenia and unexplained psychotic symptoms later in life. Marijuana is a gateway drug for addictions — you can become addicted to marijuana, and it can lead to heavier drug addictions.
• Long-term memory and attention skills
  People who use marijuana an average of ten years have poorer brain function than short term users do, even after they stop smoking the drug.

What Can I Expect Looking to the Future?

I am concerned about the trend among high schoolers to use more marijuana. Our kids need to know the risks. Supporters of legalizing marijuana point out its possible benefits — such as nausea control and pain control — but most people have a distorted understanding about the safety of this drug. The most worrisome harms are from brain injury. This can be seen long after marijuana use was active.