A Closer Look at Definium’s Phase 3 LSD for GAD Readout

Earlier this month, we covered Definium Therapeutics’ second Phase 3 readout, this time pertaining to its first LSD (DT120) for generalised anxiety disorder (GAD) study. (See Smooth Sailing: Definium’s LSD Voyage Hits Primary and Key Secondary Endpoints in GAD.)

As the dust settles on the first topline data from that program, we take a closer look through discussion with company management as well as two researchers.

Benchmarking DT120

Before we dive into specific topics that we discussed with Definium Chief Medical Officer Dan Karlin, we consulted two researchers for a broader view.

“While primary and secondary endpoints are met,” neuroscientist and entrepreneur Martijn Arns told Psychedelic Alpha, “the overall 14% remission and 43% response rates for a single dose are low when compared to other FDA approved GAD treatments”, which he said tend to deliver remission in around 28-45% of cases.

“The real question”, Arns thinks, is whether we might be “under-dosing in psychedelics trials”,  he went on, referring to the number of dosing sessions.

 “Similar to results in [treatment-resistant depression] from Compass Pathways,” he added, “here response and remission rates tend to increase across time, with further re-treatments, which makes me optimistic that achievable remission rates could be substantially higher.” Here, Arns is referring to interim analysis of Part B of the study.

He acknowledged that we will have to wait to observe in the post-approval context, and noted that follow-up data “have many caveats such as some level of selection bias, and trials not being powered for them”. Still, he said that “it is interesting to see similar trends across studies now”, which he says “somewhat challenges the idea that a single treatment would be sufficient.”

To Arns’ comparison to approved GAD treatments, we went back to an earlier version of Definium’s investor presentation to retrieve a figure that did just that. Adding the Voyage data into that April 2026 graphic seems to indeed suggest its single-dose efficacy is similar to those marketed, chronically-dosed medicines at various timepoints (from 4 weeks through to 28 weeks), albeit on the HAM-A change front.

It's perhaps unsurprising, then, that Definium has...