The former sprinter joined Warriors in February but never played a first-team game. The 24-year-old joined from the US sevens squad in the hope of adapting to the 15-a-side game but the highlight of his spell in Scotland was helping Glasgow to win the Melrose Sevens.
Gregor Townsend, the Glasgow head coach, said: "Carlin has come in and trained really well with us, but he has decided he would like to concentrate on sevens and we respect that. It's an exciting time for the sport, with it set to debut at the Olympics in 2016. We'd like to thank Carlin for coming over and we wish him all the best for the future."
Isles added: "I'd like to thank Glasgow Warriors for giving me the opportunity to train with them over the last few months. I've learnt so much from the experience and made some really good friends. However, I want to focus on sevens."