- Drinking grapefruit juice changes how long it takes some medicines to be broken down in the body. Researchers have found that a substance in grapefruit juice called DHB contributes to this effect. Some dietary supplements contain DHB and claim to increase the absorption of any and all supplements, medicine or any other drug. But these usually contain a lot more DHB than a glass of grapefruit juice. Researchers want to study the effects of grapefruit juice and supplements with DHB.