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Topic Contents

Clozapine

Drug Information

Clozapine is an atypical neuroleptic used to control symptoms of schizophrenia when other treatments are ineffective.

Common brand names:

Clozaril, FazaClo

Summary of Interactions with Vitamins, Herbs, & Foods

Types of interactions: Beneficial Adverse Check

Replenish Depleted Nutrients

  • L-Tryptophan

    Some people who take clozapine become mentally depressed after taking the drug for a few weeks. Studies have shown that clozapine can reduce blood levels of the amino acid L-tryptophan, which is often deficient in people with depression .1 More controlled research is needed to determine whether the interaction is significant and whether individuals taking clozapine might benefit from supplemental L-tryptophan or 5-hydroxytryptophan (5-HTP).

  • Selenium

    One controlled study showed that taking clozapine can decrease blood levels of selenium, a mineral with antioxidant activity.2 While more research is needed to determine whether people taking clozapine might require selenium supplementation, until more information is available, some health practitioners recommend supplementation.

Reduce Side Effects

  • Vitamin C

    Clozapine can inhibit the formation of immune cells that protect the body from invading organisms. Test tube studies show that N-acetyl-cysteine and vitamin C block the formation of immune cell–damaging compounds produced when clozapine is broken down.3 Controlled studies are necessary to determine whether supplementing N-acetyl-cysteine and vitamin C might prevent harmful side effects in people taking clozapine.

  • N-Acetyl Cysteine

    Clozapine can inhibit the formation of immune cells that protect the body from invading organisms. Test tube studies show that N-acetyl-cysteine and vitamin C block the formation of immune cell–damaging compounds produced when clozapine is broken down.4 Controlled studies are necessary to determine whether supplementing N-acetyl-cysteine and vitamin C might prevent harmful side effects in people taking clozapine.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.

Support Medicine

  • Ginkgo
    In one study, treatment with 120 mg per day of Ginkgo biloba extract for 12 weeks enhanced the beneficial effect of clozapine on certain symptoms of schizophrenia in patients who had not responded adequately to clozapine by itself5.

Reduces Effectiveness

  • Glycine

    The use of glycine may interfere with the efficacy of clozapine as an antipsychotic drug. In a double-blind trial, people with chronic, treatment-resistant schizophrenia were given clozapine (400–1,200 mg per day) and either glycine (30 g per day) or placebo for 12 weeks.6 The combination of clozapine and glycine was not effective at decreasing symptoms. In contrast, participants who took clozapine without glycine had a 35% reduction in some symptoms. Therefore, the combination should be avoided until more is known.

Potential Negative Interaction

  • Foods with Caffeine

    Caffeine is a compound found in coffee, colas, and tea, as well as in some over-the-counter products. One 31-year-old woman taking clozapine who consumed nearly 1,000 mg of caffeine daily experienced side effects from the drug.7 A subsequent study involving individuals with schizophrenia who were stabilized on clozapine, showed that caffeine avoidance resulted in significantly lower blood levels of the drug.8 Controlled research is needed to determine whether problems might occur when individuals taking clozapine change the amount of caffeine they consume each day. Until more information is available, individuals taking clozapine should talk with their healthcare practitioner before making changes in their caffeine intake.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.

Explanation Required 

  • none

The Drug-Nutrient Interactions table may not include every possible interaction. Taking medicines with meals, on an empty stomach, or with alcohol may influence their effects. For details, refer to the manufacturers’ package information as these are not covered in this table. If you take medications, always discuss the potential risks and benefits of adding a new supplement with your doctor or pharmacist.

References

1. Meltzer HY. Clinical studies on the mechanism of action of clozapine: the dopamine-serotonin hypothesis of schizophrenia. Psychopharmacology 1989;99 Suppl:S18–27 (Berlin).

2. Williams DP, Pirmohamed M, Naisbitt DJ, et al. Neutrophil cytotoxicity of the chemically reactive metabolite(s) of clozapine: possible role in agranulocytosis. J Pharmacol Exp Ther 1997;283:1375–82.

3. Linday LA, Pippenger CE, Howard A, Lieberman JA. Free radical scavenging enzyme activity and related trace metals in clozapine-induced agranulocytosis: a pilot study. J Clin Psychopharmacol 1995;15:353–60.

4. Linday LA, Pippenger CE, Howard A, Lieberman JA. Free radical scavenging enzyme activity and related trace metals in clozapine-induced agranulocytosis: a pilot study. J Clin Psychopharmacol 1995;15:353–60.

5. Doruk A, Uzun O, Ozsahin A. A placebo-controlled study of extract of ginkgo biloba added to clozapine in patients with treatment-resistant schizophrenia. Int Clin Psychopharmacol 2008;23:223-7

6. Potkin SG, Jin Y, Bunney BG, et al. Effect of clozapine and adjunctive high-dose glycine in treatment-resistant schizophrenia. Am J Psychiatry 1999;156:145–7.

7. Wetzel H, Anghelescu I, Szegedi A, et al. Pharmacokinetic interactions of clozapine with selective serotonin reuptake: differential effects of fluvoxamine and paroxetine in a prospective study. J Clin Psychopharmacol 1998;18:2–9.

8. Odom-White A, deLeon J. Clozapine levels and caffeine. J Clin Psychiatry 1996;57:175–6.

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