New research shows the harmful cardiovascular effects of one minute of exposure to secondhand smoke (SHS) from marijuana lasts three times longer than secondhand smoke from cigarettes.
The study by University of California San Francisco researchers also shows SHS from marijuana diminishes blood vessel function to the same extent as tobacco.
In a healthy person, increased blood flow causes arteries to widen in a process known as flow-mediated dilation (FMD). Blood flow is impeded when FMD is compromised during SHS exposure, and the risks of heart attack, atherosclerosis and other heart problems increase, said UCSF's Matthew Springer, Ph.D., professor of medicine and senior author of the study.
"Your blood vessels can carry more blood if they sense that they need to pass more blood to the tissues," said Springer. "They dilate to allow more blood through. But that's inhibited by exposure to smoke."
Previous work by Springer and others has shown as little as one minute of exposure to tobacco SHS diminishes FMD, but the effects of marijuana SHS hadn't been examined.
In the new research, a team of scientists in Springer's laboratory measured rats' FMD, which works similarly to FMD in humans, before and after exposure to both tobacco SHS and marijuana SHS.
They found that rats exposed to marijuana SHS experienced a more than 50 percent reduction in FMD, similar to the reduction in artery function seen in both rats and humans exposed to tobacco smoke in previous studies.
As with tobacco, the reduction occurred after just one minute of exposure to SHS from marijuana.
While rats exposed for one minute to tobacco SHS recover within 30 minutes (an observation reproduced in the new study) one minute of exposure to marijuana SHS still significantly affected FMD 90 minutes after the initial exposure.
The study fills a void in SHS research as marijuana studies are difficult to undertake because of its illicit status and the numerous agencies such as the Drug Enforcement Agency and the Food and Drug Administration that must approve the use of the drug in experiments.
"The biggest reason that people believe marijuana secondhand smoke is harmless is because the public health community hasn't had direct evidence of its harmful effects like it does with tobacco," said Springer said.
"We hadn't done the experiments, so I think there is definitely an underestimation of how harmful marijuana smoke is."