Potstock88 makes an excellent point and you can see where things...

Potstock88 makes an excellent point and you can see where things can get murky when you get a drug that is likely to have multiple effects because it modulates key endogenous molecules like IGF-1 that lead to a multitude of phenotypic changes. The Neuren website has a good Science page covering the underlying hypotheses

https://www.neurenpharma.com/science/science-behind-neuren-s-products

Animal models would provide evidence for this but they're not looking at human brains and measuring IGF-1 levels there with and without the drug or measuring alterations in synaptic connections etc. How much of each effect then is responsible for the real world patient outcomes with symptoms that are themselves a bit fuzzy to measure compared with say the size of a tumour makes it impossible to pin down a definitive MOA. Neuren use the term on their website but it would remain as more a working hypothesis I believe that is adequate to progress to market.