It would be very hard to overdose on CBD. Clinical trials have used 800 mg up to 1500 mg a day with no fear of overdosing. GW pharmaceuticals, the maker of a CBD seizure medication called Epidiolex, suggests an upper limit of 20 milligrams of CBD per kilogram of body weight per day (20 mg/kg). For a 150-pound person this would equate to about 1400 mg a day, but that does not mean that taking more means you are overdosing. However some studies have used up to 50 mg/kg which would make that 1400 mg turn into 3500 mg, an exceptionally high dose. There is some cause for concern with the liver with more information on below.