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Thioridazine

Also indexed as: Mellaril®

Thioridazine is used to treat symptoms associated with psychosis; depression with worry and restlessness in adults; irritability, worry, and fear in elderly; and severe behavioral problems in children, including fighting and hyperactivity. It is classified as a phenothiazine neuroleptic.

Interactions with Dietary Supplements

Vitamin A
A review of people taking thioridazine showed that they had higher blood levels of vitamin A than did individuals not using the drug.1 More research is necessary to determine whether taking vitamin A supplements with thioridazine might cause dangerously high vitamin A levels. Until more is known, people taking thioridazine should exercise caution with vitamin A supplementation and be alert for side effects such as bone pain, headaches, dry scaly skin, and hair loss.

Potassium
Some people taking thioridazine experience changes in the electrical activity of the heart, which sometimes improve with potassium supplementation.2 More research is needed to determine if people taking thioridazine might prevent heart problems by supplementing with potassium.

Niacin (nicotinic acid)
In a controlled study, individuals taking thioridazine for psychosis cooperated better and withdrew less from other people when niacin, 300–1,500 mg each day, was added.3 Whether people who are taking thioridazine for other mental health problems might benefit from niacin supplementation is unknown.

Coenzyme Q10
Phenothiazine drugs like thioridazine can cause changes in heart activity in some people, which might be prevented with coenzyme Q10 supplementation.4 Therefore, some doctors and pharmacists may recommend coenzyme Q10 supplements to individuals taking thioridazine.

Lithium
Lithium is a mineral that may be present in some supplements and is also used in large amounts to treat mood disorders such as bipolar disorder (manic depression). One study reviewed four cases in which individuals stabilized on lithium medication developed side effects such as delirium, seizures, and abnormal electrical activity in the brain when thioridazine was added.5 Further research is needed to determine whether similar side effects might occur in individuals taking thioridazine and supplemental lithium.

Vitamin C
Taking phenothiazine drugs can stop menstruation in some women. A 45-year-old woman taking thioridazine started menstruating once she began supplementing with 6 grams of vitamin C daily.6 Controlled studies are needed to determine whether women taking thioridazine, who are experiencing menstrual changes, might benefit from supplemental vitamin C. Vitamin C might also enhance the effectiveness of neuroleptic drugs, such as thioridazine, in the treatment of schizophrenia. One uncontrolled study showed that 10 of 13 individuals experienced a reduction in disorganized thoughts, hallucinations, and suspicious thoughts when 8 grams of vitamin C was added to their daily drug therapy.7 Controlled studies are needed to determine whether people taking thioridazine for schizophrenia might benefit from vitamin C supplementation.

Interactions with Foods and Other Compounds

Alcohol
Drinking alcoholic beverages while taking thioridazine may enhance the actions of alcohol, such as drowsiness, dizziness, and lack of concentration,8 and should be avoided. Two individuals withdrawing from chronic alcohol consumption experienced serious changes in heart function when they were given thioridazine;9 therefore, the drug should be used with caution in people who are attempting to quit drinking.

Summary of Interactions for Thioridazine

Depletion or interference Vitamin A
Adverse interaction Lithium*
Side effect reduction/prevention Coenzyme Q10
Potassium*
Supportive interaction Niacin*
Reduced drug absorption/bioavailability None known
Other (see text) Vitamin C*

For the convenience of the reader, the information in the summary is categorized as follows: “Depletion or interference” indicates the drug may deplete or interfere with the absorption or function of the supplement or herb. “Adverse interaction” indicates that the supplement or herb used together with the drug may result in undesirable effects. “Side effect reduction/prevention” indicates the supplement or herb may reduce the likelihood and/or severity of a potential side effect caused by the drug. “Supportive interaction” indicates the supplement or herb may support or aid the function of the drug. “Reduced drug absorption/bioavailability” indicates that the supplement or herb may decrease the absorption and/or activity of the drug in the body. An asterisk (*) next to an item in the summary indicates that the interaction is supported only by weak, fragmentary, and/or contradictory scientific evidence.

References:

1. Curtis JL. Effects of medication on plasma vitamin A concentrations. Clin Chem 1976;22:695.

2. Sydney MA. Ventricular arrhythmias associated with use of thioridazine hydrochloride in alcohol withdrawal. Br Med J 1973;4:467.

3. Lehmann HE, Ban TA, Saxena BM. Nicotinic acid, thioridazine, fluoxymesterone and their combinations in hospitalized geriatric patients. Can Psychiatr Assoc J 1972;17:315–20.

4. Kishi T, Makino K, Okamoto T, et al. In Yamamura Y, Folkers K, Ito Y, eds. Biochemical and Clinical Aspects of Coenzyme Q, Volume 2. Amsterdam: Elsevier/North Holland Biomedical Press, 1980, 139–57.

5. Spring GK. Neurotoxicity with combined use of lithium and thioridazine. J Clin Psychiatry 1979;40:135–8.

6. Kanofsky JD, Kay SR, Lindenmayer JP, Seifter E. Ascorbic acid action in neuroleptic-associated amenorrhea. J Clin Psychopharmacol 1989;9:388–9 [letter].

7. Beauclair L, Vinogradov S, Riney SJ, et al. An adjunctive role for ascorbic acid in the treatment of schizophrenia? J Clin Psychopharmacol 1987;7:282–3.

8. Sifton DW, ed. Physicians Desk Reference. Montvale, NJ: Medical Economics Company, Inc., 2000, 1973–4.

9. Sydney MA. Ventricular arrhythmias associated with use of thioridazine hydrochloride in alcohol withdrawal. Br Med J 1973;4:467.