If you are currently being treated with any of the following medications, you should not use vitamin B2 supplements without first talking to your health care provider.

Anticholinergic Drugs -- Used to treat a variety of conditions, including gastrointestinal spasms, asthma, depression, and motion sickness, these drugs may inhibit the body's ability to absorb riboflavin.

Tetracycline -- Riboflavin interferes with the absorption and effectiveness of tetracycline, an antibiotic. (All vitamin B complex supplements act in this way.) You should take riboflavin at a different time during the day from when you take tetracycline.

Tricyclic Antidepressants -- Tricyclic antidepressants may reduce levels of riboflavin in the body. In addition to raising levels of the vitamin in the body, taking riboflavin may also improve the effects of these antidepressants. They include:

• Imipramine (Tofranil)
• Desimpramine (Norpramin)
• Amitriptyline (Elavil)
• Nortriptyline (Pamelor)

Antipsychotic Medications -- Antipsychotic medications called phenothiazines (such as chlorpromazine or Thorazine) may lower riboflavin levels.

Doxorubicin -- Riboflavin may deactivate doxorubicin, a medication used for the treatment of certain cancers. In addition, doxorubicin may deplete levels of riboflavin in the body. Your doctor will let you know whether you need to take a riboflavin supplement or not.

Methotrexate -- Methotrexate, a medication used to treat cancer and autoimmune diseases such as rheumatoid arthritis, can inhibit the body from using riboflavin.

Phenytoin -- Phenytoin (Dilantin), a medication used to control epileptic seizures, may affect riboflavin levels in the body.

Probenecid -- This medication used for gout may decrease the absorption of riboflavin from the digestive tract and increase the excretion in the urine.

Thiazide Diuretics -- Diuretics (water pills) that belong to a class known as thiazides, such as hydrochlorothiazide, may cause you to excrete more riboflavin in your urine.