"My stomach is upset after I take CDB oil 1000ml via tincture. Should I be taking it once daily, or throughout the day? Should I take with or without food?"
There's a lot of potential components at play here but the first thing I would suggest is that many patients find their medications more effective when used throughout the day instead of as a single dose. I personally recommend splitting your dose into 3 portions - am, afternoon, and pm - so that you are consistently metabolizing the medications. If your approach to dosing is 3x/day, as opposed to more acute need single or "one off" dosing, then you could take your CBD oil with food to hopefully reduce the stomach upset. I would also consider the plant sourcing, extraction methodology, other ingredients, concentration and lab test results of the medication you are taking...while that's a lot to consider, it may be useful information to assess this stomach upset response.