When used as directed by the manufacturer, the B vitamins in Neurobion Forte are generally safe and do not produce negative effects. However, if you take more Neurobion Forte than is indicated on the bottle, you may experience adverse effects such as diarrhea. A lot of urinating might also be an indication of possible kidney damage. If you experience either of these effects, stop taking Neurobion Forte and call your doctor immediately. Rarely, some people have a reaction to vitamin B complexes. This can be anything from hives to an allergic reaction that causes difficulty breathing or swelling of the lips, tongue, or throat. If you experience any symptoms like these after taking Neurobion Forte, stop using it and call your doctor immediately. Vitamin B complexes can also sometimes cause nausea, vomiting, and abdominal pain. These effects are usually mild and go away by themselves without any treatment. But if you experience severe symptoms such as persistent nausea or vomiting, then stop taking Neurobion Forte and see your doctor immediately. People who are allergic to any ingredient in Neurobion Forte should not use it. Tell your doctor about any allergies you have so he/she can advise you which product will be right for you.