The negatives of protein powder usually stem from consuming too much protein than the body can process.
Some of the side effects you can experience from taking on excess protein include nausea, fatigue, and headaches. You can also dehydrate yourself from consuming too much protein and not drinking enough liquids along with it.
Aside from leading to an overconsumption of protein though, protein powders can be packed full of ingredients which can cause your body harm. Sugar for example is commonly seen in many protein powder blends, and consumed in excess can obviously be an issue. This can ring especially true if you are taking the powder in an already sweetened drink.
You also have to be careful of artificial ingredients and stimulates which are added, that might affect your body in different ways. This can even include substances like steroids, so it’s worth taking a thorough look at the label before you decide to invest in a protein powder.