Grapefruit and grapefruit juice are known to interact with many different prescriptions medications via several mechanisms. Perhaps most significantly, grapefruit inhibits the CYP3A metabolizing enzyme. Inhibition of this enzyme can decrease metabolism of certain medications, potentially increasing concentrations to dangerous levels. 

In addition to CYP3A inhibition, studies have shown that grapefruit also inhibits OATP (organic anion transporting peptide), an important drug transporter. OATP transports drugs into cells and when inhibited, drugs may have significantly decreased effects.

Zoloft (Sertraline) Grapefruit Interaction

There is a known interaction between grapefruit (and grapefruit juice) and Zoloft (sertraline). Grapefruit has been shown to affect Zoloft (sertraline) concentrations via inhibition of the CYP3A enzyme. Inhibition of this enzyme can potentially elevate Zoloft (sertraline) levels in the body, increasing the risk of adverse reactions. It is generally recommended not to consume significant amounts of grapefruit while on Zoloft (sertraline) due to the potential interaction. At the very least, it is recommended not to significantly alter your grapefruit intake from normal to avoid fluctuating Zoloft (sertraline) levels.

Having said all of the above, it is currently not well know how significant the interaction really is. One study suggests that while Zoloft (sertraline) metabolism is likely affected by grapefruit intake, in most cases, it isn't clinically significant. Zoloft (sertraline) is metabolized in our bodies by multiple enzymes and, according to the study, "[there is] no single agent that could substantially alter the pharmacokinetics of sertraline...".

If you are looking to avoid the potential interaction between grapefruit and Zoloft (sertraline), it is important to know that it only takes a small amount of grapefruit consumption to alter metabolizing enzyme levels. One study showed that it takes at most one whole grapefruit or 200 mL (about seven ounces) of juice to cause a clinically important interaction for most medications. However, as discussed above, it is unclear just how significant the interaction is with Zoloft (sertraline).