Grapefruit Interaction With Bipolar Drugs

Grapefruit can interfere with the metabolism of certain drugs, including bipolar medications. As a result, eating grapefruit or drinking grapefruit juice when taking these medications can inadvertently increase their concentration to potentially toxic levels.

Bipolar drugs are not the only ones affected. Also on the list of medications impacted by grapefruit are those used to treat everything from high cholesterol and arrhythmia to allergies and intestinal diseases. Even Viagra can be impacted by grapefruit consumption.

Why Grapefruit Juice Affects Drugs

A number of psychotropic drugs, including those used to treat anxiety, depression, and psychosis, are among the agents grapefruit juice may interact with. This is because grapefruit contains furanocoumarins, an organic compound that blocks an enzyme that normally breaks down these medications (the CYP3A4 enzyme).

When this enzyme is blocked, the concentration level of the drug in the blood will be higher than expected. This can make the intended effect and side effects of the drug stronger—even dangerous.

While other citrus fruits like pomelos, limes, and Seville oranges also contain furanocoumarins, they haven't been studied as closely.

Effects of Mixing Grapefruit With Medications

The degree to which grapefruit can affect certain drugs can vary. For some medications, one small glass of juice can result in what would be equivalent to a double or triple dose.

For example, as much as 99% of BuSpar (buspirone) is normally metabolized before the drug enters the bloodstream. As demonstrated in past research, when taken with grapefruit juice, the concentration can increase by 400% or four-fold.

Although it is purely speculative to suggest who the most vulnerable patient would likely be, people over 45 years old are the prime purchasers of grapefruit and receive the most prescriptions for drugs.

Medications Grapefruit Can Affect

All told, there are over a dozen drugs commonly used to treat symptoms of bipolar disorder that are known to be affected, in differing degrees, by grapefruit:

• Anafranil (clomipramine)
• BuSpar (buspirone)
• Elavil (amitriptyline)
• Halcion (triazolam)
• Luvox (fluvoxamine)
• Prozac (fluoxetine)
• Seroquel (quetiapine)
• Serzone (nefazodone)
• Tegretol (carbamazepine)
• Trazodone (desyrel)
• Valium (diazepam)
• Versed (midazolam)
• Zoloft (sertraline)

Lamictal (lamotrigine) is one bipolar medication that does not appear to interact with grapefruit juice. However, it's always best to check with your prescribing physician or pharmacist to make sure.

Before You Mix Grapefruit With Medications

Drugs that will interact with grapefruit have these defining elements:

• It is taken orally.
• It has low bioavailability.
• It is metabolized by the cytochrome P450 3A4 enzyme (CYP3A4).
• It has a narrow therapeutic index.

Always read the medication's packet insert to understand which interactions can occur. Typically, you can find this in or around the fifth paragraph, where it would read: "Talk with your doctor before including grapefruit or grapefruit juice in your diet while you are taking this medicine." 

Each year, more drugs are identified as having a possible interaction with grapefruit. However, you may still be able to enjoy grapefruit or grapefruit juice if taken according to your physician's instructions. Alternatively, you may be able to substitute other citrus fruits or drinks to obtain health benefits.