The US Food and Drug Administration has warned that there are more than fifty prescription and over-the-counter drugs in the US that can have negative affects when taken with grapefruit.

According to the administration, as little as one cup of juice or two grapefruit wedges can alter the way your medicines work and in some cases cause an overdose.

Grapefruit can delay, decrease, or enhance absorption of certain drugs, resulting in incorrect dosages and potentially dangerous drug levels in the body.

The chemicals found in grapefruit can also interfere with transporters in the intestine that help absorb drugs, nullifying any positive effects.

Help may be at hand, however, as programmes are currently underway to breed hybrid grapefruits that will be safe to mix with medications.

Until such time, the FDA has warned patients to read medication guidelines, check labels to ensure other fruit drinks do not include grapefruit and avoid Seville oranges and tangelos, which affect the same enzyme as grapefruit juice.

Drugs that are affected include orally administered sleeping drugs such as triazepam (Mogodon), diazepam (Valium), alprazolam (Xanax) and quazepam.

Other drugs affected include some statins such as atorvastatin (Lipitor), lovastatin (Mevacor) and simvastatin (Zocor, Simlup, Simcor, Simvacor).

The pain killer Codeine is also indirectly affected by reducing the amount converted by CYP3A4 into norcodeine, thus increasing the amount metabolised into morphine.

Image: Grapefruit causes problems when taken with many common medications.