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Tacrine

Also indexed as: Cognex®

Tacrine is used to treat Alzheimer’s disease and is in a class of drugs known as acetylcholinesterase inhibitors.

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.

Summary of Interactions for Tacrine

Depletion or interference None known
Adverse interaction Huperzine A*
Side effect reduction/prevention Milk thistle
Vitamin C*
Supportive interaction None known
Reduced drug absorption/bioavailability None known

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. 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.