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Willie Nelson -- one of the most prolific pot puffers on the planet -- has given up smoking weed after recent health issues ... but he still gets high.

The 86-year-old recently sat down with KSAT-TV to talk life on the road ... and his weed obsession. Willie says, "I have abused my lungs quite a bit in the past, so breathing is a little more difficult these days and I have to be careful."

Then, he drops a bombshell, saying, "I don't smoke anymore, take better care of myself."

A source close to Willie says it's true, he's not smoking weed ... however, he still vapes and eats cannabis-infused items. We're told it's also not out of the question that Willie will decide to smoke again in the future.

As for Willie's overall health, our source says he's just fine ... and is excited to continue touring through next year.