Stop Eating 'Sexy Pavement Lichen,' Scientists Warn

Botanists are raising the alarm about a common lichen being used as an alternative to Viagra.

Xanthoparmelia scabrosa, a type of lichen that grows in New Zealand and the Pacific, naturally produces PDE5 inhibitors, which block an enzyme that constricts blood flow. PDE5 inhibitors are also used in erectile dysfunction drugs like Viagra, Cialis and Levitra, which work to increase blood flow to the penis.

The fungus "contains a chemical somewhat analogous to Viagra—and somewhat toxic," lichenologist Allison Knight, who coined the phrase "sexy pavement lichen" to refer to the species, told Newsroom. "I always say in my talks that I don't recommend going out and licking the footpath."

But that hasn't stopped multiple e-commerce sites from selling extracts of sexy pavement lichen as a treatment for erectile dysfunction. Chinese e-commerce site Alibaba has nearly 400 different varieties of lichen powder available.

An analysis of one revealed it wasn't lichen at all, but rather ground Viagra mixed with grass clippings to appear natural.

Lichen on pavement
Lichen and moss on rocks Getty Images

That's because growing commercial lichen is extremely time-consuming, says Knight, "Most lichens grow very slowly, just a few millimeters per year, so it would be scarcely sustainable to harvest them."

Xanthoparmelia scabrosa doesn't even grow in China, making retailers' claims even more dubious.

Some New Zealanders are trying to go straight to the source, eating the lichen off their sidewalks and footpaths. That's not advisable, says Knight—in addition to its innate toxicity, the lichen can be contaminated with animal urine and feces or other common urban pollutants like mercury and lead. One of the evolutionary advantages of Xanthoparmelia scabrosa is its ability to withstand such toxic substances.

Although lichen's usefulness as a male sexual aid is doubtful, Knight is bullish about its scientific potential in general. "Lichens make over 1,000 unique chemicals, mainly for their own protection," she says. "Sunscreens, antibiotics, antifungals, antibacterials, anti-algal, anti-moss, insect repellents, [anti-inflammatories], dyeing agents—the list goes on."

She's currently preparing a three-part guide to the variety of lichens found in New Zealand.

Lichens are fascinating creatures—though they look like plants, they're actually "composite organisms" created by algae or bacteria in a symbiotic relationship that live suspended in filaments of fungus.

Scientists estimate that 6 percent of the Earth's surface is covered in lichens, which can grow on nearly any surface.

Natural erectile dysfunction products have been on the market for years. Some questionable Viagra substitutes include red ginseng and epimedium, known commercially as "horny goat weed."