Six schoolboys had to be treated in hospital after taking Viagra pills in their lunch break.
One of the Year Eight pupils, all aged 12 and 13, is believed to have taken the anti-impotency tablets to the all-boys comprehensive school in Berkshire and handed them around to five of his friends.
Teachers at the Forest School in Winnersh called 999 when word spread of what they had done.
A spokeswoman from Wokingham District Council, the local education authority, said: "It is believed that a pupil brought the tablets from home into the all-boys school and shared them with five friends. The school responded quickly to the situation and, as a precaution, paramedics were called.
"The pupils were taken to the Royal Berkshire Hospital in Reading. All six have subsequently been discharged and are not expected to suffer any ill-effects.
"All of the tablets have been accounted for. The school has a strict no drugs policy and a pupil will be temporarily excluded for actions which placed other pupils at risk."
The incident happened on October 16.
Viagra was launched by Pfizer in 1998 as a breakthrough in the treatment of male impotency and is a prescribed drug, although it is available for sale on the internet.
Sexual health experts have said the effects of the drug on young people are untested and side effects unknown.
Although it is not thought the boys will be seriously affected, doctors say any reaction with other medication could be dangerous.