Folbiol 5 mg, a folic acid supplement, is generally safe, but like all medications, it can cause side effects. Common side effects may include nausea, stomach upset, loss of appetite, or a bitter taste in your mouth. Rare but more serious side effects can include allergic reactions, skin rashes, or difficulty breathing. If you experience any severe or persistent side effects, it's crucial to consult with your doctor immediately. Always inform your healthcare provider about any existing medical conditions or medications you're taking before starting Folbiol.