Up to 40% of patients taking clonidine (Catapres) will experience dry mouth and about a third will have drowsiness, headache, and sleepiness. Other common side effects include constipation, dizziness, and local skin reactions with use of the Catapres-TTS skin patch. Reserpine use is linked with possible side effects including nightmares , stuffy nose, depression , and an inability to fall asleep. Diarrhea and heartburn are also possible. Guanadrel and guanethidine can cause diarrhea and other gastrointestinal issues – as well as dizziness and drowsiness.
Severe deficiency of niacin in the diet causes the disease pellagra , which is characterized by diarrhea, dermatitis, and dementia, as well as Casal's necklace lesions on the lower neck, hyperpigmentation, thickening of the skin, inflammation of the mouth and tongue, digestive disturbances, amnesia, delirium, and eventually death, if left untreated.  Common psychiatric symptoms of niacin deficiency include irritability, poor concentration, anxiety, fatigue, restlessness, apathy, and depression.  Studies have indicated that, in patients with alcoholic pellagra, niacin deficiency may be an important factor influencing both the onset and severity of this condition. Patients with alcoholism typically experience increased intestinal permeability , leading to negative health outcomes.