Tacrine is used to treat Alzheimer’s disease and is in a class of drugs known as acetylcholinesterase inhibitors.
Summary of Interactions with Vitamins, Herbs, and Foods
In some cases, an herb or supplement may appear in more than one category, which may seem contradictory. For clarification, read the full article for details about the summarized interactions.
 May be Beneficial: Side effect reduction/prevention—Taking these supplements may help reduce the likelihood and/or severity of a potential side effect caused by the medication. | Milk thistle Vitamin C* |
 Avoid: Adverse interaction—Avoid these supplements when taking this medication because taking them together may cause undesirable or dangerous results. | Huperzine A* |
| Depletion or interference | None known |
| Supportive interaction | None known |
| Reduced drug absorption/bioavailability | None known |
An asterisk (*) next to an item in the summary indicates that the interaction is supported only by weak, fragmentary, and/or contradictory scientific evidence.
Interactions with Dietary Supplements
Vitamin C
Tacrine can cause reversible liver damage in some people who take the drug. Test tube studies have shown that vitamin C blocks the formation of cell-damaging substances produced when tacrine is broken down by the body.1 Controlled studies are needed to determine whether supplemental vitamin C might prevent liver damage in people taking tacrine.
Interactions with Herbs
Huperzine A
Further studies are needed to determine the long-term safety of huperizine A. Until more is known about its actions in the body, it is best to avoid using it together with tacrine, which also prevents the breakdown of acetylcholine.
Milk thistle (Silybum marianum)
Tacrine often causes elevations of a liver enzyme in the blood that indicates potential liver damage. One double-blind trial showed that taking 420 mg each day of silymarin, a compound found in milk thistle, together with tacrine did not prevent liver enzyme elevation. However, silymarin did reduce the number of people who developed more severe enzyme elevations. In addition, silymarin reduced adverse stomach and intestinal side effects that are common in individuals taking tacrine.2 Therefore, supplementing with milk thistle or silymarin may be considered as a possible way to reduce the adverse effects of tacrine.
Interactions with Foods and Other Compounds
Food
Controlled studies show that the absorption of tacrine is significantly reduced when taken with food.3 Consequently, tacrine should be taken an hour before or two hours after a meal unless stomach or intestinal upset occurs.
Smoking
Smoking cigarettes increases the elimination of tacrine from the body.4 This may be a problem for people who either start or stop smoking while taking the drug. Those who start smoking may experience a reduction in the beneficial effects of tacrine, while those who stop smoking might experience more side effects.
References
1. Madden S, Woolf TF, Pool WF, Park BK. An investigation into the formation of stable, protein-reactive and cytotoxic metabolites from tacrine in vitro. Studies with human and rat liver microsomes. Biochem Pharmacol 1993;46:13–20.
2. Allain H, Schuck S, Lebreton S, et al. Aminotransferase levels and silymarin in de novo tacrine-treated patients with Alzheimer’s disease. Dement Geriatr Cogn Disord 1999;10:181–5.
3. Welty DF, Siedlik PH, Posvar EL, et al. The temporal effect of food on tacrine bioavailability. J Clin Pharmacol 1994;34:985–8.
4. Zevin S, Benowitz NL. Drug interactions with tobacco smoking. An update. Clin Pharmacokinet 1999;36:425–38.
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2006-09-07
