Red clover supplementation seems to be quite safe when used for up to 3 years.[1][2] Most trials have not found significant side effects compared to placebo,[3][4] although larger clinical trials are needed to properly evaluate side effect risk.
The concentration and type of active compounds in red clover can vary depending on how the plant was grown and processed, which can impact its effects on the body.[5][6] This can result in inconsistent effects when using different extracts of red clover. Variability in effect may also be seen between people due to differences in genetics and the gut microbiome, both of which can impact how isoflavones are metabolized in the body.[7]