The three most common oral decongestants are pseudoephedrine, phenylpropanolamine and phenylephrine. These work by shrinking blood vessels in the nose, thus reducing congestion. Unfortunately, their effect is not confined to the nose as decongestants can worsen hypertension (high blood pressure), Raynaud's phenomenon and can act as a stimulant. Due to this last side effect, decongestants are frequently combined with sedating antihistamines . However, the stimulant and sedative effects do not alway cancel each other out, resulting in an upset in one's daily cycle.