Projectile with Potion Effects also affects shooter

So Im having this issue a lot of times and for a while and I don't know how to solve 'it. As the tittle says, when creating a ranged weapon or item that shoots projectiles with potion effects, the potion also applies on the shooter.

I also added NoGravity to the projectile so they go straight.

I have read that if I use the if then else procedure it can be achieved, but I do not understand how it works or what I have to put. 

I have also read that in the projectile code in the tick() section it should appear, but I understand code and I would not know write it out.

If you could help me with that by adding images I would appreciate it.

Thanks for your time