Please always let your doctor know what you are already taking and ask him if the additional 5mg would be too much. Are you sure it's 5mg (=5000 micrograms) though? Prenatal vitamins usually contain 400 micrograms (=0,4mg) or 800 micrograms (=0,8mg).
From the NHS website: "What happens if I take too much folic acid? Taking doses of folic acid higher than 1mg can mask the symptoms of vitamin B12 deficiency, which can eventually damage the nervous system if it's not spotted and treated." https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-b/
@Meis 5mg is prescription strength and is recommended in certain cases such as high BMI.
@Charley I see... I'd still ask the doctor just to be sure.
It's ok to take together. You will wee out any surplus