Inhaling secondhand marijuana smoke for just a minute may damage blood vessels, a new study in rats has found. Researchers found that rats' blood vessels took at least three times longer to recover function after only a minute of breathing secondhand marijuana smoke, compared to recovery after a minute of breathing secondhand tobacco smoke. When rats inhaled secondhand marijuana smoke for one minute, their arteries carried blood less efficiently for at least 90 minutes, whereas similar exposure to secondhand tobacco smoke caused blood vessel impairment that recovered within 30 minutes, researchers said. "While the effect is temporary for both cigarette and marijuana smoke, these temporary problems can turn into long-term problems if exposures occur often enough and may increase the chances of developing hardened and clogged arteries," said Matthew Springer from University of California in the US. Blood vessel function was examined in rats before and after exposure to secondhand marijuana smoke at levels similar to real-world secondhand tobacco smoke. "Arteries of rats and humans are similar in how they respond to secondhand tobacco smoke, so the response of rat arteries to secondhand marijuana smoke is likely to reflect how human arteries might respond," said Springer. Researchers also found the mere burning of the plant material appears responsible for the impaired blood vessels, not chemicals like nicotine and tetrahydrocannabinol (THC), the psychoactive ingredient in marijuana, nor rolling paper. The inhalation of smoke should be avoided, regardless of whether it comes from tobacco, marijuana, or other sources. Inhaling smoke is bad for you, researchers said. The findings were published in the Journal of the American Heart Association.