Synthroid is available in many forms -- tablets, capsules, solution, and intravenous Levothyroxine. Read the patient information leaflet if available from the pharmacist before you start consuming the medication. If you have any questions, ask your physician or pharmacist. Here are the directions for its usage:

• Administer Synthroid on an empty stomach as a single dose, preferably one hour before breakfast.
• Avoid taking Synthroid along with other medicines, especially those containing iron and calcium. Take it four hours before or after taking the other medicines as they may affect the absorption of Synthroid.
• Take the doses recommended by your doctor, as the quantities are based on your age, body weight, and condition.
• Crush the tablet of Synthroid when it needs to be given to infants and children incapable of swallowing an intact tablet. Mix it in a small quantity (one to two teaspoonfuls) of water and give it using a spoon to the child. Never store the crushed tablet or water mixture, and do not give this medication with any soybean-based infant formula as it may lead to a severe interaction.3
• Avoid taking Synthroid along with antacids.
• You should use this medication daily or as prescribed by your physician to obtain the maximum benefit of the treatment.  Try to take the medication at the same time daily. 
• Do not stop taking this medication without consulting your doctor. Thyroid replacement treatment is often prescribed for a very long period.
• Do not switch to other brands without consulting your physician. 
• In case of missed dose: Take Synthroid the moment it is possible. However, leave out the missed dose if it is nearly the time for the next dose. Avoid taking two doses at one time.