Sam Altman's longevity startup is upping the dose in an Alzheimer's drug trial after a lackluster first round

Joe Betts-LaCroix is the CEO of Retro Biosciences, a longevity biotech company backed by Sam Altman.

Retro Biosciences Retro Biosciences, a longevity startup funded by Sam Altman, is testing an Alzheimer's pill.

The medicine is designed to clear out gunk that builds up in the brain as we age.

In healthy volunteers, no major side effects have been detected, the company said.

The Sam Altman -funded longevity startup Retro Biosciences is testing a longevity pill that the company hopes could one day fight dementia.

First, however, they need to figure out the right dose.

The pill, called RTR 242, is designed to jump-start key cellular recycling processes in the body, which stall as we get older, and get especially clogged up in people with neurodegenerative diseases, including Alzheimer's and Parkinson's.

RTR 242 has already been in clinical trials in Australia for several months, a bullish attempt to beat the longevity-focused competition in Silicon Valley.

Things are going well, Retro CEO Joe Betts LaCroix told me, when I showed up at the company's bustling office in Redwood City.

No major side effects, no safety signals.

But that presents a challenge: Retro scientists can't pinpoint the dose at which they'll get the best results: enough medication to be potent, but without severe side effects.

"It's sort of like a curse and a blessing for us, in that it makes it a little bit hard to measure that 'Yay; it's doing the thing,'" Betts-LaCroix said.

So, Retro is adding two new cohorts to their safety trial, the CEO told Business Insider in an exclusive interview.

They're increasing total enrollment in their Phase 1 trial by more than 42%, from 76 to 108 participants.