According to the source novels, Percy was indeed receiving counselling for his ADHD prior to learning about his godly powers.
I have moments like that a lot, when my brain falls asleep or
something, and the next thing I know I’ve missed something, as if a
puzzle piece fell out of the universe and left me staring at the blank
place behind it. The school counsellor told me this was part of the
ADHD, my brain misinterpreting things.
Percy Jackson and the Lightning Thief
Evidently it's not uncommon for other demigods to go through the same thing, since their abilities come across very strongly as ADHD. No counselling is offered at Camp Half-Blood and it certainly seems to be discouraged to take medication to help with the symptoms.
‘You don’t know anything about me.’
‘No?’ She raised an eyebrow. ‘I bet you moved around from school to school. I bet you were kicked out of a lot of them.’
‘How –’
‘Diagnosed with dyslexia. Probably ADHD, too.’
I tried to swallow my embarrassment. ‘What does that have to do with anything?’
‘Taken together, it’s almost a sure sign. The letters float off the page when you read, right? That’s because your mind is hardwired for ancient Greek. And the ADHD – you’re impulsive, can’t sit still in the classroom. That’s your battlefield reflexes. In a real fight, they’d keep you alive. As for the attention problems, that’s because you see too much, Percy, not too little. Your senses are better than a regular mortal’s. Of course the teachers want you medicated. Most of them are monsters. They don’t want you seeing them for what they are.’
‘You sound like… you went through the same thing?’
‘Most of the kids here did. If you weren’t like us, you couldn’t have survived the Minotaur, much less the ambrosia and nectar.’
Percy Jackson and the Lightning Thief
Percy goes on to embrace this diagnosis.
I tried to skim through Chiron’s stack of reports as we walked. There
were messages from demigods, nature spirits and satyrs all around the
country, writing about the latest monster activity. They were pretty
depressing, and my ADHD brain did not like concentrating on depressing
stuff.
Percy Jackson and The Last Olympian