Britain's Ministry of Defence says five soldiers whose duties sometimes included guarding the queen were dismissed from the army after they failed drug tests.
The ministry said today that the soldiers were part of the King's Troop Royal Horse Artillery.
The unit is based in London and is responsible for firing the 41-gun salute in royal parks to celebrate royal events, including the queen's official birthday.
They also participate in the ceremony of Trooping the Colour on June 16 and the state opening of Parliament in mid-November.
The army says it will not tolerate drug misuse in its ranks.