The high profile Botswanan athlete tested positive for the banned stimulant methylhexaneamine after a struggling fourth in the 400m final in Glasgow.
A CGF statement confirmed: “On 29th July a test during the Commonwealth Games produced an adverse analytical finding indicating the presence of Methylhexaneamine Dimethlypentaylamine – a substance prohibited under the current WADA Prohibited List – Class S6 Stimulants.
“Ms Montsho requested that her B sample be analysed, which subsequently confirmed the initial A sample analysis.
“The results of all her performances at the Games will now be nullified.”
Montsho, who won the world title in 2011 and finished second behind Christine Ohuruogu in Moscow last year, accepted the drug test findings, the CGF added.
The CGF has passed on their decision to the sport’s governing body the IAAF to decide what further action to take against her.
Montsho was the most high profile athlete to fail a drugs test at the Games, which also saw 16-year-old Nigerian weightlifter Chika Amalaha stripped of her gold medal.
Montsho arrived in Glasgow as defending Commonwealth 400m champion, but she missed out on a medal behind a Jamaican cleansweep led by Stephanie McPherson.
The three-time African champion is a mainstay on the Diamond League circuit and her victory at the 2011 Daegu worlds saw her become Botswana’s first world or Olympic track and field champion.