What is a good value of N in human research?

Hi my mighty /sci/
From a paper...

>This double-blind, counterbalanced, placebo-controlled study (n= 26) assessed the acute mood and cognitive effects throughout the day of four different doses (37.5mg, 75mg, 150mg and 300mg) of a standardised guaraná extract (PC-102).

When you come from invertebrates research and used to see something like (n=14000) and now see that NOOBISH "n".

What I should do? Trust that low N?

>>1
quality of humans important

whites, n = 20 sufficient

mongoloid races, n  = 40 required

all others (mud) n >= 100 or better