Patients should consult their physician before taking any additional prescriptions, over-the-counter medications, nutritional supplements or herbal medications. Interactions of particular concern to individuals taking psoriasis medications depend on the medication taken and may include:

• Grapefruit juice. Grapefruit juice interferes with the liver’s ability to rid the body of some substances. This could lead to a buildup of chemicals in many oral psoriasis medications (e.g., methotrexate) to toxic levels in the body. Though the buildup is less likely if the juice is ingested four or more hours before taking the medicine, patients are generally advised to refrain from drinking grapefruit juice. There is no indication that eating grapefruit (as opposed to drinking juice) presents any danger to patients.
  
  
• Retinoids. Alcohol should not be used with oral (by mouth) retinoids.
  
  
• Vitamin D analogs. Antacids, mineral oils and certain cholesterol medications may alter the absorption of some vitamin D analogs in the skin. Some antiseizure medications may reduce the activity of certain vitamin D analogs whereas corticosteroids may counteract their effects.
  
  
• Methotrexate. Must not be taken with nonsteroidal anti-inflammatory drugs (e.g., ibuprofen) as this greatly increases medication toxicity and can be fatal. Other drugs that may increase the toxicity (and therapeutic effects) of methotrexate and should be avoided include salicylates (drugs used to relieve pain and reduce fever) and sulfonamides (a class of antibiotics). Immunizations may not be effective when taking methotrexate. Oral antibiotics and folic acid may reduce the effectiveness of this medication. Alcohol should not be used with methotrexate.
  
  
• Other immunosuppressants. Immunosuppressant medications are typically not administered with other immunosuppressants because they may excessively suppress the immune system.
  
  
• Psoralens. Should not be taken with foods that contain furocoumarin (e.g., carrots, celery, figs, limes, mustard, parsley, parsnips) or medications that increase photosensitivity (e.g., coal tar products, retinoids, sulfonamides, tetracyclines, other psoralens). Some psoralens may result in abnormal liver function tests.