League of Legends FPS Lag spikes

I've Played League for a while now but i hate to keep having this Fps Lag Spike in my game. At the start of the game im running a solid 60 fps and even higher for a while but then around 5-10 minutes i start to have a massive drop in fps to 29 fps but then sometimes randomly its brought back to 60. Can someone please tell why and possible solution for this problem.