Clonidine is a medication used to treat high blood pressure, ADHD, and other conditions. While clonidine can cause some side effects, such as low blood pressure and dizziness, it is not known to cause tachycardia (a rapid heart rate). In fact, clonidine can actually help reduce heart rate and blood pressure in some cases. However, it is important to follow your doctor’s instructions and report any concerning symptoms or side effects while taking clonidine.