Research into the long-term safety of and optimal dosing for MCTs in humans is limited, which emphasizes the need for further research.[1] However, MCTs are generally considered safe to consume, and toxicity is unlikely.[1][2][3][4][5] That said, some supplementation studies have reported side effects like nausea, diarrhea, and abdominal discomfort.[6][1]
The no-observed-adverse-effect level (NOAEL) for MCTs ranges from 3 to 5 grams per kg of body weight per day.[6] However, people who received MCTs via intravenous infusion (e.g., people who received total parenteral nutrition (TPN)) have tolerated dosages of 3 to 9 grams per kg of body weight (gram/kg) per day for several months without adverse effects.[6] To put this in context, a standard 2,500 calorie-per-day diet in which 30% of calories come from dietary fat would include about 80 grams of fat per day. If all 80 grams were derived from MCTs, then the daily MCT intake in a 70-kg person would be approximately 1.1 grams/kg, which is far lower than the NOAEL range. However, a typical daily intake of MCTs in the diet is only around 2 to 9 grams per day, and someone who takes a daily MCT supplement will likely only ingest 5 to 20 grams per day; these ranges are also much lower than the NOAEL of 210 to 350 grams per day for a 70-kg (154-lb) person.
It is also important to note that, in general, the evidence underpinning the benefits of MCTs has a moderate to high risk of bias because there are few studies with small sample sizes and/or poor methodological quality (e.g., lacking a control group) and were funded/authored by manufacturers of MCT-containing supplements.