In 1991, David G. Bailey, PhD., discovered that taking grapefruit juice with blood pressure medication stopped the body from properly absorbing the drugs, rendering them ineffective at best and creating a toxic overdose at worst. Now, Bailey has discovered the problem goes beyond grapefruit juice, and doctors are recommending patients stick with a glass of water for taking pills.

A slew of drugs ranging from allergy medications to chemotherapy drugs interact poorly when taken with juice, diminishing their effectiveness or blocking them out altogether.

"A normal amount of grapefruit or several other citrus fruits consumed even many hours beforehand has the potential to cause unintentional overdose toxicity of more than 40 medications. Recently, we discovered that grapefruit and other fruit juices substantially decreased the oral absorption of drugs undergoing intestinal uptake transport," Bailey said. "The concern is loss of benefit of medications essential for the treatment of serious medical conditions."

Many prescription medications have labels warning consumers against drinking grapefruit juice, and now apple and orange juice might join their fellow fruit on the sticker.

Grapefruit juice contains a substance called naringin, which researchers found slows down an enzyme in the liver that processes at least 40 drugs. The result of the slow processing could mean that a normal pill could turn into an overdose. Orange juice contains a similar compound, probably hesperidin, while the substance in apple juice remains unknown, Bailey said.

Researchers gave subjects fexofenadine, an allergy drug and had them ingest it with either a glass of water, a glass of grapefruit juice, or a glass of water containing naringin. The patients taking the grapefruit juice and the naringin absorbed half as much as the drug as patients drinking water.

Some of the drugs with absorption affected by grapefruit juice include: the allergy drug fexofenadine, sold as Allegra; the antibiotics ciprofloxacin, sold as Cipro and Proquin, levofloxacin, sold as Levaquin, and itraconazole sold as Sporanox; the beta-blocker blood pressure drugs atenolol, sold as Tenormin; celiprolol, and talinolol, the transplant-rejection drug cyclosporine, sold as Gengraf or Neoral; and the cancer chemotherapy etoposide, sold as Toposar or Vepesid, the WebMD report said.

After news of the research broke, several doctors recommended that patients take their medication with a glass of water and avoid drinking juices for at least two hours afterward.