Do not give Sudafed to a child younger than 4 years old. Always ask a doctor before giving a cough or cold medicine to a child. Death can occur from the misuse of cough and cold medicines in very young children.
Ask a doctor or pharmacist before using any other cough or cold medicine. Pseudoephedrine or other decongestants are contained in many combination medicines. Taking certain products together can cause you to get too much of a certain drug. Check the label to see if a medicine contains pseudoephedrine or a decongestant. Do not use Sudafed if you have used an MAO inhibitor such as furazolidone (Furoxone), isocarboxazid (Marplan), phenelzine (Nardil), rasagiline (Azilect), selegiline (Eldepryl, Emsam, Zelapar), or tranylcypromine (Parnate) in the last 14 days. A dangerous drug interaction could occur, leading to serious side effects.
Before taking this medicine
Do not use Sudafed if you have used an MAO inhibitor such as furazolidone (Furoxone), isocarboxazid (Marplan), phenelzine (Nardil), rasagiline (Azilect), selegiline (Eldepryl, Emsam, Zelapar), or tranylcypromine (Parnate) in the last 14 days. A dangerous drug interaction could occur, leading to serious side effects. Do not use Sudafed if you are allergic to pseudoephedrine or to other decongestants, diet pills, stimulants, or ADHD medications.
Ask a doctor or pharmacist if it is safe for you to take Sudafed if you have:
heart disease or high blood pressure;
diabetes; or
a thyroid disorder.
FDA pregnancy category C. It is not known whether Sudafed will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant while using Sudafed. Pseudoephedrine can pass into breast milk and may harm a nursing baby. Do not use Sudafed without telling your doctor if you are breast-feeding a baby.
Artificially sweetened liquid cold medicine may contain phenylalanine. If you have phenylketonuria (PKU), check the medication label to see if the product contains phenylalanine.
 Sudafed Congestion pregnancy and breastfeeding warnings (more detail)
