The pupil brought the drugs into St Kevin's Primary School on the Falls Road without the knowledge of its staff.
An ambulance was called to the school after the child became drowsy.
The child has recovered fully and a letter has been sent to all parents.
A statement from the school said: "A child took tablets into school and unfortunately took some of these tablets while in school.
"At no stage was anyone aware that the child had these tablets in school.
This was an isolated incident which has been handled appropriately and responsibly by all involved and reported to the relevant agencies.
St Kevin’s Primaryu School
"The class teacher responded immediately when it became apparent that the child had ingested something.
"The child's parents were called and an ambulance was requested. The incident was handled quickly, appropriately and reported to the relevant agencies."
The statement added: "The children's safety and well being is of paramount importance to St Kevin's."
SDLP councillor Colin Keenan has said that the school has taken the appropriate measures.
He said: "I want to commend the staff for dealing with the exceptional discovery of drugs in the possession of a young child earlier this week.
"The staff dealt with this exceptional set of circumstances in a swift and professional way.
"I have spoken to a number of parents of children attending St Kevin's and they are satisfied that the school is taking appropriate action to deal with this upsetting incident.
"It is right that the school is going to have awareness training for both teachers and pupils so that the entire school community can be better educated about the perils of drug use."