Do not tame a low level giga its not worth the time or narcotics to tame it. A low level giga has very bad stats such as a low damage and stamina and health. My tribe tamed a level 15 giga and it sucks trust me go big or go home.
Beware Gigas get nerfed once tamed so if tame try taming a lvl 140+ or whatever is max lvl wild spawn in your server a 20 giga have around 80 k health in wild and will one shot your dinos but once tamed will be reduced to 17k health and superless attributes like 400 stamina which is total shit
Honestly, I would just tame a charcharodontosaurus. Gigas are hard to tame, and a low level giga after taming it has crappy stats. It also has no special attacks! All it has is a roar that does nothing and a chomp that does practically nothing. On the other hand, the charchar has a blood rage effect that boosts healing and damage, And a blood frenzy that increases speed. It also has a tail spin and roar that speeds up nearby tames. And it’s relatively easy to tame too. So I would just tame a charchar instead of wasting all those tranq arrows and darts on a giga.