The recommended oral dose of muira puama appears to be 1000-1500mg of a 4:1 concentrated extract (equivalent to 4,000-6,000mg of the basic extract). It is unsure if this is the optimal dose or whether it needs to be taken with a meal.
100-300mg/kg appears to be the active range for anti-stress and anxiolytic effects in rats, which converts to an estimated human equivalent of:
1,100-3,300mg for a 150lb person
1,500-4,400mg for a 200lb person
1,800-5,500mg for a 250lb person
These are currently the recommended intakes as the higher end of the recommendation is similar to what is recommended to humans that appears to be effective.