There are actually several potential side effects to Gatorade when not used properly. Gatorade has high levels of vitamins, sodium, sugar, and consequently calories.
Respectively, overuse of fortified drinks such as Gatorade can result in vitamin toxicity, especially with Vitamin A which cannot be flushed from your system in large quantities. This can cause nausea, fatigue, blurred vision, and headaches. This is would require a significant amount of Gatorade, however, and is not common.
The high levels of sodium can also result in increase blood pressure, as with any high sodium products. This can lead to increased risk for heart attacks and strokes.
The high sugar content can caused increased blood sugar which can be extremely dangerous for people who are diabetic, but also affects non-diabetics as well. That, coupled with the calorie content, can caused increased weight gain due to the way blood sugar works in the body.
There is also some risk of hyponatremia according to some research, which is over hydration of cells. You normally hear about this when runners drink too much water and their cells get over hydrated. Products like Gatorade help stem this off by adding sodium along with the water, but too much can still throw off the normal cellular balance which can ultimately end in death. This requires, however, extremely large amounts of Gatorade, but it is still not recommended to drink more than a bottle or two per heavy workout.
These effects are exacerbated by the context in which you consume these products. They are designed as replenishment product and should not be consumed except for when your body has expended a considerable amount of energy. If you body's resources aren't depleted then adding these fortified ingredients will just saturate your body with more than it is designed to handle, which can result in any of the previous conditions.
Gatorade is a vitamin-enriched sports drink that helps in rehydrating your body quickly and also improves athletic performance under conditions of extreme physical exertion. It is a well balanced mixture of water, sugar (carbohydrates), and salts (electrolytes). Research has shown that for athletic competitions, Gatorade is very effective in preventing dehydration and has no adverse side effects. However, drinking too much Gatorade can have serious health consequences, and weight gain too.