Drug-induced flushing reaction is characterized by episodic erythema and warmth of the head, neck, and arms associated with the use of a medication or other drug. Flushing is an involuntary response of the central nervous system that increases cutaneous blood flow. Onset is hours to days after initiation of medication. Common medications that trigger a flushing reaction include nicotinic acid (niacin), vasodilators, calcium channel blockers, nitroglycerin, anti-inflammatories, cholinergics, beta blockers, and angiotensin-converting enzyme (ACE) inhibitors. Other drugs, including opiates, amyl nitrite, butyl nitrite, cocaine, heroin, alcohol, and amphetamines, as well as alcohol combined with drugs, can cause severe reactions with flushing.

Certain medications known to cause moderate drug-induced flushing reaction, such as infused vancomycin, may be treated by giving patients diphenhydramine and famotidine, then restarting vancomycin at a reduced dosage.

Some medications, such as antiestrogen medications, can induce a pharmacologic menopause reaction. Withdrawal from hormone replacement therapy can also induce a flushing reaction.

Serotonin syndrome is a potentially life-threatening condition caused by excess serotonergic activation. Be sure to ask about medications that may have serotonergic effects within the central nervous system. These drugs include serotonin reuptake inhibitors, tricyclic antidepressants, monoamine oxidase inhibitors, and opiates. Other medications such as triptans, antibiotics, antiemetics, cough syrups, herbal remedies, or illicit drugs can cause serotonin syndrome in the setting of serotonergic medications listed previously. Serotonin syndrome is a clinical diagnosis and encompasses a spectrum of disease. Classically, serotonin syndrome is composed of a triad of mental status changes, autonomic hyperactivity, and neuromuscular abnormalities. The spectrum of disease ranges from benign to lethal and may be missed.

Alcohol is a common cause of "dry flushing" in patients with aldehyde dehydrogenase gene polymorphisms. A deficiency in aldehyde dehydrogenase causes an increase in acetaldehyde levels, which slows alcohol metabolism and causes a cutaneous flushing reaction. Patients may also report dizziness, lightheadedness, fatigue, anxiety, headache, weakness, nausea, or vomiting associated with alcohol intake. Even in the absence of an aldehyde dehydrogenase gene polymorphism, alcohol combined with medications can cause a flushing reaction. Those medications include disulfiram, chlorpropamide, metronidazole, ketoconazole, griseofulvin, cephalosporins, chloramphenicol, antimalarials, and topical tacrolimus.