Propranolol (Inderal) and other beta-blockers (eg. Lopressor, Tenormin, Congard, etc.) make the hyperthyroid patient feel better by blocking the action of thyroid hormone – the heart rate slows, and nervousness and shaking are reduced – and are used until the thyroid hormone T4 level returns to normal.

Propranolol:
• May make asthma worse.

• May hide the warning signs of low blood sugar – important for diabetics to know.

• Can interfere with the growth of your baby if taken during pregnancy – its use should be limited.

• Can cause breathing problems for the baby at birth if taken during the last few weeks of pregnancy.

• May cause heart muscle contractions in a patient with heart failure (rare).

• Make sure you never run out of this drug. If Propranolol is stopped suddenly it may:
- worsen angina in patients who have coronary artery disease;
- trigger hyperthyroidism in a hyperthyroid patient.

• You cannot donate blood if you are taking Propranolol.

To avoid the above complications from abruptly stopping Propranolol, your doctor will reduce your dosage gradually over several weeks when you no longer need to take it.