Clinical signs of hyperthyroidism may occur in case of overdose, if the individual tolerance limit for levothyroxine is exceeded, or if the dose is increased too fast at the start of treatment. The following symptoms are typical: tachycardia, palpitation, cardiac arrhythmias (e.g. atrial fibrillation and extrasystoles), angina pectoris, headache, muscular weakness and cramps, flushing, fever, vomiting, disorders of menstruation, pseudotumour cerebri, tremor, restlessness, insomnia, hyperhidrosis, weight loss, diarrhoea.
In such cases the daily dose has to be reduced or the medication withdrawn for several days. Therapy may carefully be resumed once the adverse reactions have disappeared.
In case of hypersensitivity to any of the ingredients of Euthyrox allergic reactions, particularly of the skin, may occur. Cases of angioedema have been reported.