A review of potential side effects in humans found that CBD was well tolerated across a wide dose range, up to 1500 mg per day orally. Though it’s often well-tolerated, CBD can cause side effects such as dry mouth, diarrhea, reduced appetite, drowsiness, and fatigue. CBD can also interact with other medications you’re taking, such as blood thinners, so always check with your doctor when starting CBD if you have prescriptions.