Medicine & USMLE

Phenylephrine and Pseudoephedrine

Sympathomimetics and Sympatholytics (Old)
  1. Dopamine
  2. Fenoldopam
  3. Dobutamine
  4. Epinephrine
  5. Norepinephrine
  6. Isoproterenol
  7. Midodrine
  8. Phenylephrine and Pseudoephedrine
  9. (Alpha) Methyldopa
  10. Clonidine (and Guanfacine)
  11. Tizanidine


Phenylephrine and pseudoephedrine are drugs that act as agonists or activators at alpha-1 receptors. Activation of these alpha-1 receptors can be used to treat nasal congestion as well as hypotension or shock by way of inducing vasoconstriction. These drugs are also used in ophthalmic procedures to induce mydriasis.

Key Points

  • Phenylephrine, Pseudoephedrine
    • Mechanism of Action
      • Alpha 1 > Alpha 2
        • Alpha 1 Effects: Increases IP3 and DAG  through Gq GPCR → Vasoconstriction → Increased TPR → Increased Blood Pressure
    • Clinical Use
      • Hypotension
        • Vasoconstriction increases TPR to increase Blood Pressure
      • Ocular Procedures (Mydriasis)
        • Activation of iris dilator muscle leads to mydriasis
      • Rhinitis/Congestion
        • Decreased blood flow causes nasal tissue to shrink, thereby clearing the congestion
      • Ischemic priapism
    • Adverse Effects
      • Hypertension
        • Vasoconstriction increases TPR to increase Blood Pressure
      • CNS Stimulation
        • Excess adrenergic stimulation in the CNS (like amphetamines and cocaine)
      • Rebound congestion
        • Downregulation and desensitization of alpha 1 receptors in the vessels of the nasal mucosa leads to diminished effect of phenylephrine