Talk:Grapefruit

Grapefruit juice enhances the effect of some commonly used medications by increasing their bioavailability or half life via the selective down-regulation of a specific subfamily of the cytochrome P450 enzyme system in the small intestine- most notably CYP3A4. This effect can be seen with a single grapefruit or 200mL of grapefruit juice, and persist for as much as 3 days.

Grapefruit-drug interactions typically cause increased amounts of the drug in the body, however in a few cases it can cause a decrease.

A number of recreational drugs are affected by grapefruit. Notable examples include:

• Most benzodiazepines - although the effect may be very minor depending on the specific drug.
• Ketamine - when used intranasally or orally, but not when used IM or IV, has increased absorption and duration from grapefruit.
• Oxycodone - which can have the half life increased by 50%
• Methadone - but only to a very small extent.
• Codeine - is metabolised into inactive norcodeine by CYP3A4. Grapefruit inhibits CYP3A4, so more morphine is produced, which might be dangerous
• Buprenorphine - but the extent of the effect is unknown.
• Other opioids - may also be affected but more research is needed.
• Erectile dysfunction drugs Viagra, Cialis and Levitra show somewhat increased blood levels.
• Cocaine - serum levels may be increased, but has not been well studied.
• DXM - is metabolised into inactive 3-MM by CYP3A4. Grapefruit inhibits CYP3A4, so more DXO is produced, which is also metabolised by CYP3A4.

If one chooses to combine grapefruit with recreational drugs, it may also affect non-recreational drugs, including:

• Estradiol - Grapefruit and grapefruit juice decrease the breakdown of estrogen in the body
• Fexofenadine - Fexofenadine is transported into the body by OATP1A2, which is inhibited by grapefruit