3-2 gram per day divided

Clinical Evidence [from ConsumerLab] [my annotations]

In one study of women with recurrent UTIs, a dose of 1 gram of D-mannose three times a day for 2 weeks, and then 1 gram twice a day for 5 months, resulted in significantly more women remaining free of infection compared to ongoing treatment with antibiotics (trimethoprim/sulfamethoxazole) (Porru, J Clin Urol 2014).

In another study, 2 grams of D-mannose powder (U-tract, Progressive Laboratories) taken with water once every evening for six months worked as well as ongoing treatment with the antibiotic nitrofurantoin to reduce the rate of recurring urinary tract infection in women.