<p>Fluphenazine reverses antihypertensive effects of Guanethidine, Methyldopa and Clonidine. It also causes lithium toxicity by interacting with it. Antacids may reduce bioavailability of phenothiazines. Additive CNS depressant effects produced with alcohol, barbiturates, hypnotics, sedatives, opiates and antihistamines.</p>