Cigarette Ads Once Promised Absurd Health Benefits. Scientists Just Found One of Them Was Actually True.

Here’s what you’ll learn when you read this story:Before cigarette advertisements were regulated by the federal government, companies made lots of crack-pot health claims.However, one such claim has held up under scientific scrutiny: Smokers are less likely to develop Parkinson’s disease.The cause isn't cigarettes, but low-dose carbon monoxide—one of the 7,000 chemicals in cigarette smoke. Before the federal government required stark, black-and-white warning labels on cigarette packaging, tobacco companies often marketed their addictive wares with laughable health claims by modern standards. In 1930, a doctor named Edward Roehrig claimed that Thompson’s Mell-O-Well cigars were the “health cigar” (he later tragically died of lung cancer).Jay Paull//Getty ImagesA 1937 advertisement by Philip Morris claimed that their cigarettes cleared up “every case of irritation of the nose and throat due to smoking” caused by other brands. And a 1946 ad said Camels were supposedly the brand of choice for doctors nationwide (and the same ad also perplexingly proclaimed that cigarettes were good for your “T-zone”).Apic//Getty ImagesHowever, in 1959 scientists did make a cigarette health claim that remained remarkably true for decades—regular smokers were less likely to develop Parkinson’s Disease (PD). When burned, cigarettes create more than 7,000 chemicals, according to the American Lung Association, so the immediate cause for this inexplicable finding was initially difficult to pin down. Previous studies ruled out the addictive ingredient nicotine as a possible answer, but in recent years, scientists have begun circling one potential culprit: carbon monoxide.That seems counterintuitive, since we install detectors to guard against the odorless, colorless gas. But the dose makes the poison, and a new JAMA Neurology study of more than 500,000 Chinese adults links exhaled CO levels to Parkinson’s outcomes.“Laboratory and animal studies have suggested that low doses of CO might protect the brain,” Oxford University’s Clara Bueno Lopez, lead author of the study, wrote for The Conversation. “Until now, though, no large-scale human study has combined measurements of people’s CO levels with information on whether they later developed Parkinson’s.”In 2024, a study in the journal npj Parkinson’s Disease linked low-dose carbon monoxide with reduced risk of PD among smokers because the concentration of hemoglobin-bound CO is higher in smokers than non-smokers. And, somewhat counterintuitively, low-dose CO can actually reduce oxidative stress and inflammation while also activating neuroprotective signaling.The new study adds further evidence that carbon monoxide drives the protective effect. Lopez and her team found that people with elevated exhaled CO who had never smoked also had a lower risk of PD, suggesting the benefit has nothing to do with cigarettes—and everything to do with the gas itself.“CO may contribute to the lower risk of Parkinson’s seen in people who smoke, and that CO may have a protective role in Parkinson’s independent of smoking,” Lopez writes.Exhaled CO can come from outside and inside the body. Burning solid fuels for cooking or being around burning wood, coal, and petrol, can raise exhaled CO levels while human cells also make tiny amounts of CO, which in small doses can protect them while also supporting the immune system.Of course, smoking causes roughly 85 percent of lung cancer cases, so it’s not considered a viable preventative measure for Parkinson’s. But perhaps divorcing the positive effects of carbon monoxide from cigarette smoke could yield important health benefits. A San Diego-based biotech company announced the beginning of a Phase 2a clinical trial in June 2026 for an oral drug called HBI-002 that uses low-dose carbon monoxide as a form of PD therapy.“While the devastating health consequences of smoking are undisputed and overwhelming, scientists have long been intrigued by this statistical anomaly, hypothesizing that a single component within the toxic cocktail of smoke might hold a neuroprotective key,” the press release for the clinical trial says.Definitively finding that key could bring much needed relief for the 1.1 million people living with Parkinson’s disease in the U.S. alone.Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.