Serious Side Effects of Taking Diethylpropion (Tenuate) If you are experiencing any of the side effects listed, you should stop taking diethylpropion (Tenuate) immediately and seek emergency medical attention: an allergic reaction (difficulty breathing; closing of your throat; swelling of your lips, tongue, or face; or hives); an irregular heartbeat or abnormally high blood pressure (migraine or headache, [...]