Probably read 15-20 years ago. IT was a paperback in English, published in USA.
The story set when man has reached the stars. (Honor Harrington level of civilization.) I recall a bit of a story. I can't remember if the main character (MC) was male or female.
Something happens (attempt on life, or attack on family) and the parents tell the now adult children, they need to stop what ever they had been doing because it happened before.
It comes out that either the MC or their siblings had been drugged, (when they were early or mid teens) by either the parents or their enemies, with a drug that lowered intelligence. Maybe the family were royalty or big in politics and the drugging was a warning to stay out.
Maybe the parents were told, You feed this drug to the kids, and we won't try to kill them again? (Thus the parents will be too busy taking care of the kids to be involved in politics.)
I get a feeling that maybe an older brother had been drugged. (I'm not sure if the other kids were drugged.) I seem to remember him raging about, thats the reason why he had so much trouble in school, and the rest of extended family (aunts/uncles/cousins) were telling him he was stupid.
When the drugging stopped (or he became immune to the drug,) it took so long for him to catch up to his classmates who were now years ahead of him education wise.
