The 43-year-old actor said that he follows the lunar calendar to determine when it's the best time to get a trim, reported Elle magazine.
"If you want your hair to be thicker, cut it when the moon is about to be full - a heavy, full, waxing moon. Do not cut it when the moon's waning.
"Why do you think that (farmers) plant at certain times of the year? It's not hippie-dippie stuff. Look, how do they know when you reap, when you sow, when you plant?" he said.
McConaughey said that he still uses the product to this day and he swears by its ability to keep his mane in tip-top shape.
"Back in 1999, my hair was falling out, so I started (using) this stuff. And if I didn't bring my hair back so well that people thought that I went and got plugs... I believe that I'm proving the product," he said.