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

Antibiotics, Tetracycline
Riboflavin should not be taken at the same time as the antibiotic tetracycline because it interferes with the absorption and effectiveness of this medication. Riboflavin either alone or in combination with other B vitamins should be taken at different times from tetracycline. (All vitamin B complex supplements act in this way and should therefore be taken at different times from tetracycline.)

In addition, long-term use of antibiotics can deplete vitamin B levels in the body, particularly B2, B9, B12, and vitamin H (biotin), which is considered part of the B complex.

Antidepressant Medications
Tricyclic antidepressants (such as imipramine, desimpramine, amitriptyline, and nortriptyline) also reduce levels of riboflavin in the body. Taking riboflavin may improve levels of the vitamin and improve the effectiveness of these antidepressants, especially in elderly patients.

Anti-malarial Medications
Riboflavin may reduce the effectiveness of anti-malarial medications such as chloroquine and mefloquine.

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

Birth Control Medications
Poor dietary habits in combination with birth control medications can interfere with the body's ability to use riboflavin.

Doxorubicin
In the presence of daylight, riboflavin may deactivate doxorubicin, a medication used for the treatment of certain cancers. In addition, doxorubicin may deplete levels of riboflavin and, therefore, increased amounts of this nutrient may be recommended during chemotherapy using this drug. Your doctor will guide you on whether this is necessary or not.

Methotrexate
Methotrexate, a medication used to treat cancer, can prevent the body from making riboflavin (as well as other essential vitamins).

Phenytoin
Phenytoin, a medication used to control epileptic seizures, may affect riboflavin levels in children.

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

Selegiline
Similar to its effects on doxorubicin, riboflavin may deactivate selegiline, a medication used to treat Parkinson's disease, in the presence of daylight.

Sulfa-containing Medications
Riboflavin may reduce the effectiveness of sulfa-containing medications, such as certain antibiotics (for example, trimethoprim-sulfamethoxazole) used to treat bacterial infections.

In addition, as stated earlier, long-term use of antibiotics can deplete vitamin B levels in the body, particularly B2, B9, B12, and vitamin H (biotin), which is considered part of the B complex. 

Thiazide Diuretics
Diuretics that belong to a class known as thiazides, such as hydrochlorothiazide, may increase the loss of riboflavin in the urine.