It is unlikely that pure paracetamol caused your increased heart rate. However, many cold remedies combine paracetamol with decongestants (like pseudoephedrine or phenylephrine). These decongestants can interact with your thyroid medication (Thyronorm), causing a rapid heart rate. This reaction is usually temporary and not dangerous, but you should stop taking that medication. Please check the ingredient label. For safe cold relief, you can take plain paracetamol, use saline nasal sprays, or try steam inhalation. Avoid multi-symptom cold products containing decongestants. If your rapid heart rate persists or you feel dizzy, please consult your doctor.