The main adverse effects of taking exogenous ketones include headaches and gastrointestinal problems like nausea, diarrhea, flatulence, belching, heartburn, abdominal pain, and bloating.[1][2][3][4][5][6] However, these side effects are typically mild, and exogenous ketones are generally considered to be safe for consumption.[4][5][6] That said, there is a lack of studies thoroughly examining the dose-response relationship and pharmacokinetics of exogenous ketones in humans, and their safety is not fully understood.
Another drawback of exogenous ketones is that, although consuming them can mimic signs of ketosis (a raised beta-hydroxybutyrate concentration in the blood),[7][2][1][5] unlike other interventions that induce ketosis (a ketogenic diet or fasting), exogenous ketones do not cause the body to burn its own fat stores. Therefore, exogenous ketones are not a replacement for interventions designed to induce weight loss. See Do exogenous ketones cause weight loss? for more details.
It is also important to note that much of the evidence about the benefits of exogenous ketones has a moderate to high risk of bias because there are few studies,[8][9] small sample sizes,[8] inadequate reporting about randomization and blinding,[9] a high level of heterogeneity between the studies,[8][1][2] and potential conflicts of interest (studies being funded/authored by manufacturers of exogenous ketone supplements).[1][2] Furthermore, many studies use an off-the-shelf consumer product containing exogenous ketones but do not independently analyze the product to confirm its composition and purity. Doing this would increase confidence in the study findings.