My friend has very bad brain fog from a physical condition. It’s so bad she often pauses when she speaks like a YouTube video trying to buffer on a bad internet connection and she told me she wants to be more like her former self. She’s on medication for the condition, but the brain fog is one symptom that persists. She wants some good insight on how effective amphetamines are for brain fog in the non-ADHD population. She could only find people who have both ADHD and brain fog which could skew things. She doesn’t have ADHD, just brain fog.
This sounds like a sleeping disorder, imo.
And no, ADHD medications do not make you immune to brain fog. In some situations they can make it worse, especially when they wear off.
Ask your friend if they’ve been checked for sleep apnea.