Monday, December 22, 2014

Can Marijuana Prevent Cancer?

In our Healthy Kids blog last week, an adolescent specialist cited research finding that marijuana use can increase cancer risk - a connection many commenters questioned loudly. Here are the facts.

Can Marijuana Prevent Cancer?

French researchers concluded in a 2008 study that marijuana users were 2.4 times more likely to develop lung cancer than non-users. And cancer investigators in New Zealand found that the heaviest marijuana users in their 2008 study had a five-fold higher risk for lung cancer compared to non-users.  (AP Photo/Eric Risberg)
French researchers concluded in a 2008 study that marijuana users were 2.4 times more likely to develop lung cancer than non-users. And cancer investigators in New Zealand found that the heaviest marijuana users in their 2008 study had a five-fold higher risk for lung cancer compared to non-users. (AP Photo/Eric Risberg) AP

Does Marijuana Cause Cancer - or Prevent It?

Last week’s Healthy Kids post about a new study that regular marijuana use by teens dumbs down their IQs later in life raised a ruckus. Our expert panelist, adolescent specialist Rima Himelstein, MD, cited research finding that marijuana use can increase cancer risk - a connection many commenters questioned loudly.

One commenter pointed out that some studies show compounds in marijuana may have anti-cancer properties. Another contended there’s no scientific proof  that marijuana raises risk. Where’s the truth? Here’s what the research says:

1. Marijuana use is associated with higher risk for testicular cancer. In a 2011 study published in the journal Cancer,  researchers from the National Cancer Institute found that men with testicular cancer were 2.2 times more likely to be regular marijuana smokers (daily or more often) then men without this rare cancer.  A 2009 study from the Fred Hutchinson Cancer Center in Seattle  found the same thing.  Researchers aren’t sure exactly why, but note that “The exact mechanism of how heavy marijuana use might increase the risk of TGCT (testicular germ cell tumors)  is unknown, however chronic marijuana exposure has multiple adverse effects on the endocrine and reproductive systems such as gynecomastia, impotence, reduced sperm counts, and suppressed testosterone.”

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2. Marijuana more than doubles lung cancer risk. French researchers concluded in a 2008 study that marijuana users were 2.4 times more likely to develop lung cancer than non-users. And cancer investigators in New Zealand found that the heaviest marijuana users in their 2008 study had a five-fold higher risk for lung cancer compared to non-users. In general, they found that smoking one joint daily for a year raised risk slightly more than a pack-a-day smoking habit did.

3. Yes, some marijuana compounds seem to protect against cancer -- but others ding DNA and dampen immunity. Cannabinoids extracted from marijuana pushed brain-cancer cells to die faster in one 2009 Spanish study.  And a  2009 Brown University study  found lower odds for squamous-cell cancers of the head and neck among marijuana smokers.

But that’s not a great reason to light up. In 2007, Canadian researchers found levels of ammonia, hydrogen cyanide, nitric oxide and other nasty chemicals in marijuana that were three to 20 times higher than in tobacco. The researchers note that while tobacco’s toxins -- including 50 that are cancer-causing --  have been studied extensively, those in marijuana haven’t.  There’s plenty we don’t yet know.

But more is being revealed.  In 2009, another team of Canadian scientists watched what happened when they added condensed marijuana or tobacco smoke to animal cells in test tubes.  Marijuana damaged DNA more than tobacco did.  And in 2010, University of South Carolina scientists found that cannabis suppresses immunity - which could leave users’ bodies under-equipped to fight cancer.

About this blog
Anna Nguyen Healthy Kids blog Editor
Sarah Levin Allen, Ph.D., CBIS Assistant Professor of Psychology at Philadelphia College of Osteopathic Medicine
Stephen Aronoff, M.D., M.B.A. Chair of the Department of Pediatrics at Temple University Hospital
Peter Bidey, D.O. Medical Director of Family Medicine at Philadelphia College of Osteopathic Medicine
Christopher C. Chang, MD, PhD, MBA, FAAAAI, FACAAI Associate Professor of Medicine in division of Rheumatology, Allergy and Clinical Immunology at UC Davis
Katherine K. Dahlsgaard, Ph.D. Lead Psychologist of The Anxiety Behaviors Clinic at Children's Hospital of Philadelphia
Gary A. Emmett, M.D., F.A.A.P Director of Hospital Pediatrics at TJU Hospital & Pediatrics Professor at Thomas Jefferson Univ.
Mario Cruz, M.D. Pediatrician, Associate Director of Pediatric Residency Program at St. Christopher’s Hospital for Children
Magee DeFelice, M.D. Division Chief of Allergy and Immunology at Nemours/Alfred I. duPont Hospital for Children
Hazel Guinto-Ocampo, M.D. Chief of Pediatric Emergency Services at Nemours duPont Pediatrics/Bryn Mawr Hospital
Rima Himelstein, M.D. Adolescent Medicine Specialist at Crozer-Keystone Health System
Jessica Kendorski, PhD, NCSP, BCBA-D Associate Professor in School Psychology/Applied Behavior Analysis at Philadelphia College of Osteopathic Medicine
Anita Kulick President & CEO, Educating Communities for Parenting
Janet Rosenzweig, MS, PhD, MPA VP for Programs & Research for Prevent Child Abuse America
Beth Wallace Smith, R.D. Registered Dietitian at Children's Hospital of Philadelphia
Jeanette Trella, Pharm.D Managing Director at The Poison Control Center at CHOP
W. Douglas Tynan, Ph.D., ABPP Director of Integrated Health Care for American Psychological Association
Flaura Koplin Winston, M.D., Ph.D. Scientific Director of the Children’s Hospital of Philadelphia’s Center for Injury Research and Prevention
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