Serious side effects caused because of the use of Methylcobalamin+Pregabalin are uncommon and rare. However, it may cause serious side effects like allergic reaction, suicidal thoughts or swelling of limbs (hands, legs or feet). Stop taking Methylcobalamin+Pregabalin and contact your doctor if you have any signs of these serious side effects. Signs of an allergic reaction include swelling of your face, mouth, lips, gums, tongue and neck. Allergic reactions can also lead to trouble in breathing, skin rash, hives (raised bumps) or blisters. Pay attention to any changes, especially sudden changes in mood, behaviors, thoughts or feelings, or if you have suicidal thoughts.