Secondhand marijuana smoke may damage blood vessels as much as tobacco smoke

This research, led by UCSF professor Matt Springer, is being presented today (November 16, 2014) at the American Heart Association Annual Scientific Sessions.
 
Study Highlights:

  • Secondhand marijuana smoke may have similar cardiovascular effects as tobacco smoke. 
  • Lab rats exposed to secondhand marijuana smoke had a 70 percent drop in blood vessel function. 

 
CHICAGO, Nov. 16, 2014 — Breathing secondhand marijuana smoke could damage your heart and blood vessels as much as secondhand cigarette smoke, according to preliminary research presented at the American Heart Association’s Scientific Sessions 2014. 
 
In the study, blood vessel function in lab rats dropped 70 percent after 30 minutes of exposure to secondhand marijuana smoke. Even when the marijuana contained no tetrahydrocannabinol (THC) — a compound in marijuana that produces intoxication — blood vessel function was still impaired. 
 
Reduced blood vessel function may raise the chances of developing atherosclerosis and could lead to a heart attack. Atherosclerosis is the disease process that causes plaque build-up in the arteries which narrows them and restricts blood flow. 
 
“Most people know secondhand cigarette smoke is bad for you, but many don’t realize that secondhand marijuana smoke may also be harmful,” said Matthew Springer, Ph.D., senior author of the study and cardiovascular researcher and associate professor of Medicine at the University of California, San Francisco’s Cardiology Division. 
 
Marijuana and tobacco smoke are chemically and physically alike, aside from their active ingredients. 
 
The drop in blood vessel function from THC-free marijuana suggests that the compound isn’t responsible for the effect. Similarly, this study confirms that nicotine is not required for smoke to interfere with blood vessel function. 
 
In the study, researchers used a modified cigarette smoking machine to expose rats to marijuana smoke. A high-resolution ultrasound machine measured how well the main leg artery functioned. Researchers recorded blood vessel dilation before smoke exposure and 10 minutes and 40 minutes after smoke exposure. 
 
They also conducted separate tests with THC-free marijuana and plain air. There was no difference in blood vessel function when the rats were exposed to plain air. 
 
In previous tobacco studies, blood vessel function tended to go back to normal within 30 minutes of exposure. However, in the marijuana study, blood vessel function didn’t return to normal when measured 40 minutes after exposure. 
 
Now that marijuana is becoming increasingly legalized in the United States, its effect on others is a growing public health concern, Springer said. 
 
“If you’re hanging out in a room where people are smoking a lot of marijuana, you may be harming your blood vessels,” he said. “There’s no reason to think marijuana smoke is better than tobacco smoke. Avoid them both.” 
 
Secondhand tobacco smoke causes about 34,000 premature deaths from heart disease each year in the United States among nonsmokers according to the U.S. Surgeon General’s 2014 report on the consequences of smoking. 
 
More research is needed to determine if secondhand marijuana smoke has other similar effects to secondhand cigarette smoke in humans. 
 
The National Institute on Drug Abuse and the Elfenworks Foundation funded the study. 
 
Here is the abstract:
 
Brief Exposure to Marijuana Secondhand Smoke Impairs Vascular Endothelial Function 

Xiaoyin Wang, Ronak Derakhshandeh, Shilpa Narayan, Emmy Luu, Stephenie Le, Olivia M. Danforth, Hilda J. Rodriguez, Richard E. Sievers, Suzaynn F. Schick, Stanton A. Glantz, Matthew L. Springer, Univ of California, San Francisco, San Francisco, CA
 
Objectives: Despite general public awareness that tobacco secondhand smoke (SHS) is harmful, much of the public still regards marijuana SHS as benign. Because marijuana smoke and tobacco smoke are chemically and physically similar (other than nicotine and tetrahydrocannabinol (THC)), we tested this assumption by asking whether short exposure to marijuana SHS causes acute vascular endothelial dysfunction similar to that caused by tobacco SHS. Exposure to tobacco SHS impairs arterial flow-mediated dilation (FMD) in humans and rats. 
Methods: We used a rat model to test the effects of secondhand marijuana smoke on FMD. We exposed anesthetized rats to marijuana SHS using a modified cigarette smoking machine, and measured FMD three times: before 30-min exposure (“pre”), 10 min after end of exposure (“post10”), and 40 min after end of exposure (“post40”). FMD was measured by micro-ultrasound measurements of femoral artery diameter before and after transient (5 min) surgical ligation of the common iliac artery. Concentrations of respirable suspended particles <2.5 μm (RSP) fell during exposure; exposure conditions are denoted by starting concentrations. 
Results: Marijuana SHS starting at 667±62 μg/m3 RSP (n=8) caused FMD to fall from 7.5±0.94% (SEM) pre to 2.3±0.50% at post10 and 2.2±0.80 at post40 (P<0.01 for both post10 and post40 vs. pre, adjusted for multiple comparisons). SHS from placebo marijuana lacking THC starting at 671±49 μg/m3 RSP (n=7) similarly impaired FMD (9.9±1.4% pre, 4.3±0.64% post10 (p<0.01), 5.5±1.3% post40 (P<0.05)), confirming that impairment did not depend on the THC. In contrast, air in the exposure chamber (1.8±0.7 μg/m3RSP; n=8) did not alter FMD (11.0±0.64% pre, 11.4±0.72% post10, 11.7±0.86% post40, P>0.70).
Conclusions: Marijuana and tobacco SHS impair endothelial function similarly under comparable exposure conditions. Public exposure to SHS should be avoided whether the source is tobacco or marijuana.