Hi & Welcome. I can understand your concern. Since you have been taking Thyronorm 100 microgram/day, a TSH level of 5.5 is suggestive of inadequate treatment or hypothyroidism. A TSH level of 0.4-4 microgram is the desirable range to have adequate control. As long as you take Thyronorm this TSH level (0.53) should be maintained and hence for that you will have to take Thyronorm in the dose of 125 microgram. The most common side effects of Thyronorm include headache, insomnia (sleep problems), feeling nervous or irritable, fever, hot flashes, sweating, increased heartbeats, changes in your menstrual periods (if you are a female) appetite changes, weight changes, etc. Hair loss may occur during the first few months of treatment. This effect is usually temporary as your body adjusts to this medication. If this effect persists or worsens inform your doctor promptly. You must also consult your treating doctor if you get increased sweating, sensitivity to heat, mental/mood changes (such as nervousness, mood swings), tiredness, diarrhea, shaking (tremor), shortness of breath, swelling of the hands or ankle, chest pain, fast or pounding irregular heartbeats. Hope this answers your query.