Because a doctor’s prescription is not needed, many people mistakenly believe over the counter (OTC) medications are safer than prescription and street drugs. They are safe and effective when taken as directed; however, OTC medications can cause serious and potentially fatal side effects when abused. When taken in different quantities than recommended or when symptoms aren’t present, OTC medications may affect the brain in ways very similar to illegal drugs. For a description of the most commonly abused OTC medications and their side effects, click on the links below.