Phenylephrine HCl does not normally have any adverse side effects when used as directed. However, mild pain may occur if the rectal tissue is bleeding. If the pain persists or worsens, you must quickly call a doctor. Some people may experience rare side effects such as headache, irregular heartbeat, shakiness, nervousness, and trouble sleeping. Mineral oil may slow down the absorption of vitamins A, D, K, and E. If you are taking medications that contain mineral oil then you may consider taking vitamin supplements. Mineral oil may reduce the effectiveness of some oral contraceptives. You must consult a doctor before using the product. Whether you use Preparation H Hemorrhoidal Ointment for internal or external hemorrhoids, you must consult a doctor if you have high blood pressure, thyroid disease, heart disease, or diabetes.