A week before he was sworn in as secretary of the US Department of Health and Human Services in February, a video of anti-vaccination conspiracy theorist Robert F Kennedy Jr went viral.

In it, Kennedy, who has frequently promoted debunked health claims, is seen squirting inky blue liquid into a drinking glass. The substance was widely speculated to be a dye called methylene blue, though Kennedy has not publicly commented on it.

The fabric dye is also taken by the likes of Joe Rogan – who in a podcast weeks later said that “RFK Jr told me about it” – and Bryan Johnson, the sludge-eating American venture capitalist who has sunk millions into trying to prevent the (famously) inevitable process of death.

So what is methylene blue and is there any benchmark evidence that it’s good for your health?

Methylene blue is a synthetic textile dye, noted for its ability to bind well to fabrics. (Kennedy, ironically, wants the US food industry to stop using artificial dyes.)

The substance has gained popularity in wellness circles, with a laundry list of claimed benefits, including that it boosts cognition, increases energy levels, has anti-ageing effects, relieves stress and has antioxidant effects. On TikTok, influencers poke out blue tongues and dropper the cobalt colourant straight into their mouths.

But ingestion of the dye for unapproved uses carries serious risks.

Methylene blue was first synthesised in the late 19th century.........

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