5-fluorouracil
hydroxyurea
trimethoprim
sulfasalazine (used to control inflammation associated with Crohn disease, ulcerative colitis and rheumatoid arthritis)
triamterene (a diuretic)
birth control pills (also related to the duration use of birth control pills) may reduce serum folate levels but without  inducing  clinically  significant folate deficiency.When methotrexate is prescribed, folic acid supplements are sometimes given with the methotrexate. The therapeutic effects of methotrexate are due to its inhibition of dihydrofolate reductase and thereby reduce the rate de novo purine and pyrimidine synthesis and cell division. Methotrexate inhibits cell division and is particularly toxic to fast dividing cells, such as rapidly dividing cancer cells and the progenitor cells of the immune system. Folate supplementation is beneficial in patients being treated with long-term, low-dose methotrexate for inflammatory conditions, such as rheumatoid arthritis (RA) or psoriasis, to avoid macrocytic anemia caused by folate deficiency. Folate is often also supplemented before some high dose chemotherapy treatments in an effort to protect healthy tissue. However, it may be counterproductive to take a folic acid supplement with methotrexate in cancer treatment. Cerebral folate deficiency
Cerebral folate deficiency is when levels of 5-methyltetrahydrofolate are low in the brain as measured in the cerebral spinal fluid despite being normal in the blood. Symptoms typically appear at about five months of age. Without treatment there may be poor muscle tone, trouble with coordination, trouble talking, and seizures. The causes of cerebral folate deficiency include mutations of genes responsible for folate metabolism and transport.
Because the neural tube closes in the first four weeks of gestation, often before many women even know they are pregnant, many countries in time decided to implement mandatory food fortification programs. A meta-analysis of global birth prevalence of spina bifida showed that when mandatory fortification was compared to countries with healthcare professionals advising women but no mandatory fortification program, there was a 30% reduction in live births with spina bifida, with some countries reported a greater than 50% reduction.Over 80 countries require folic acid fortification in some foods. Fortification of rice is common. The USDA has required the fortification of flour since 1998. Since then, Hispanics in the United States have seen the greatest reduction of neural tube defects. Canada has mandated folic acid fortification of flour since 1998 which has resulted in a 42% decrease in neural tube defects. Fortification of wheat and corn flour, milk and rice is required in Costa Rica which has led to a reduction of neural tube defects of as much as 60%. Epidemiology
Folate deficiency is very rare in countries with folic acid fortification programs. Overall, the worldwide prevalence of anemia due to folic acid deficiency is very low. However, data on the prevalence of deficiency amongst specific high risk groups is lacking.