Tapazole

An overactive thyroid puts the body's engine into overdrive. Weight drops even though appetite is good, the heart pounds or races, hands tremble, sleep breaks up and heat becomes hard to bear. Graves' disease, an autoimmune condition that drives the gland to overproduce, is the commonest cause. Methimazole is the tablet that reins it in, and it is also used to steady hormone levels before thyroid surgery or radioactive iodine treatment.

How the tablets work

Methimazole blocks thyroid peroxidase, the enzyme the gland uses to build iodine into thyroxine and triiodothyronine. While the drug is on board, no fresh hormone is assembled. The gland still holds a stock of finished hormone that trickles out, so the benefit shows over the first few weeks rather than in a day.

Taking your tablets

The tablets are taken three times a day, about eight hours apart, each dose with a meal. Food, or a glass of milk when a meal is not due, makes the nausea and indigestion methimazole can cause less likely. Taking them at the same times each day keeps the level in the blood even. A late tablet is fine as long as the next dose is still hours away; when the two would land on top of each other, miss one out rather than doubling up. Blood tests for free T4 and T3 show whether the dose is right.

Side effects worth knowing about

Rash or itching, an unsettled stomach, a metallic or bitter taste, pins and needles in the hands, swollen or tender joints, drowsiness and dizziness turn up fairly often in the first weeks, and many of these ease with time. Hair may thin.

The blood count is the change that matters most. If white cells fall sharply, a sore throat, fever, chills or mouth ulcers can be the first warning, and that needs urgent treatment. Liver trouble is rare but shows itself as yellowing of the skin and the whites of the eyes, urine that turns dark, or pain in the upper right of the abdomen along with going off food.

Methimazole crosses the placenta and reaches breast milk, so it is not taken during pregnancy or while breastfeeding. Keep the tablets in their original bottle with the lid tight, out of a child's reach.

Which strength to order

Both are plain tablets of the same medicine. A 10mg tablet is double the 5mg dose, which suits a higher daily total with fewer tablets to swallow; the 5mg size lets the dose be adjusted in smaller steps.