I tried both MethylF 2 mg/day, Folinic acid 6 mg/day and Acid F 1.2 mg/day, and got very bad reaction to each one, mainly brain related (strong headache with non functionning brain), together with burning thighs' muscles. I had a look at what we can find about folates toxicity but there is very few studies about it, neurotoxicity is cited but not explained and there's no study about different folate supplements and their side effect, it's a bit frustrating : TOXICITY OF FOLIC ACID GIVEN IN PHARMACOLOGICAL DOSES TO HEALTHY VOLUNTEERS (1970) on thelancet "Abstract A trial to elucidate the effect of folic acid in pharmacological doses (15 mg. daily) on serum-vitamin-B12 levels in a group of fourteen healthy volunteers was abandoned after 1 month of a projected 3-month period because of the unexpected development of increasingly disturbing toxic effects in the majority. Most of the subjects experienced mental changes, sleep disturbance and gastrointestinal symptoms. Possible mechanisms of these effects are discussed." on cab direct, the same article is differently presented: Toxicity of folic acid given in pharmacological doses to healthy volunteers. Author(s) : HUNTER, R.; BARNES, J.; OAKELEY, H. F.; MATTHEWS, D Journal article : Lancet 1970 Vol.1 pp.61-63 "Abstract : A total of 14 healthy volunteers were given 15 mg folic acid by mouth daily. The trial was abandoned after 1 month because of toxic effects of a gastrointestinal or nervous kind. It is suggested that folic acid may have a specific effect on cerebral metabolism. If values for folacin in cerebrospinal fluid are correlated with serum folacin, then very high values for folacin in cerebrospinal fluid were probably reached because mean serum folacin values rose from 4.5 to 120 ng per ml at the end of the trial. The symptoms of folic acid intoxication observed may be related to brain-amine change, which would explain the "alerting" effect of folic acid when given to patients on anticonvulsant drugs.-M. J. B." How Safe Are Folic Acid Supplements? Article · Literature Review · August 1996 with 38 Reads DOI: 10.1001/archinte.156.15.1638 · Source: PubMed Norman R. C. Campbell "Abstract Periconceptual use of folic acid supplements by women is effective in preventing neural tube defects in the fetus. Folic acid supplements also may prevent atherosclerosis and some malignant neoplasms. Nevertheless, safety concerns have delayed recommendations to increase folic acid consumption by the general population. Among the potential safety issues of folic acid supplementation are (1) difficulty identifying cobalamin deficiency, precipitation of neurologic complications of cobalamin deficiency, and lowering of cobalamin levels; (2) folate neurotoxicity; (3) antagonism of drugs that inhibit folate metabolism; (4) reduced zinc absorption; (5) association with malignant neoplasms; (6) hypersensitivity reactions; and (7) increased susceptibility to malaria. The data that suggest that folic acid supplements are unsafe are weak and consist predominantly of case series and reports. Nevertheless, greater difficulty diagnosing cobalamin deficiency due to "masking" of hematologic abnormalities by folic acid is a potential risk. Strict vegetarians need to be informed that they are at risk of cobalamin deficiency. Physicians need to be aware that routine hematologic indexes have a low sensitivity for cobalamin deficiency, especially in patients who are receiving folic acid supplements. Because no high-quality data exclude specific adverse effects, physicians should be vigilant in identifying detrimental effects when patients increase their consumption of folic acid. Arch Intern Med. 1996;156:1638-1644"