Does levothyroxine break a fast?

Levothyroxine is a thyroid hormone tablet for an underactive thyroid. A tablet has no sugar, protein or calories that count. On the four goals this site uses to sort answers, it is safe for weight loss, blood sugar, autophagy and gut rest.

The timing rule is what links levothyroxine to fasting. Take it on an empty stomach, 30 to 60 minutes before your first meal of the day. Leave the same gap before any drink with caffeine, such as tea or coffee, and before any other medicine. The US label gives the same window of half an hour to an hour before breakfast. It also lists foods that can reduce how much of the tablet you absorb.

As a worked example, say you take the tablet with water at 7:00 and eat at 12:00 on a 16:8 schedule. Your first meal is five hours away, so the empty-stomach gap is easy to keep. Black coffee is the drink to watch. Wait until 7:30 at the earliest, or 8:00 for the full hour, before you have it.

Take levothyroxine exactly as prescribed. Never skip a tablet, change the dose or move it to fit a fasting plan. If your eating window means your usual time no longer works, ask your doctor or pharmacist how to fit the fast around the medicine.

Long-term calorie restriction lowered the active thyroid hormone T3 in one study, while TSH and T4 stayed the same. The evidence is early, and it comes from long-term eating less, not from short fasts. If you have a thyroid condition, talk to your doctor before you start fasting. Do not fast without medical advice if you are pregnant or under 18.