Thyro-L PowderThyro L is used for correction of conditions associated with hypothyroidism in horses. Thyro L contains levothyroxine sodium. Active Ingredients Levothyroxine Sodium USP. Each level teaspoonful contains approximately 12mg of T4. Directions for User Thyro L can be administered by mixing the daily dose in the concentrate or by administering once with grain, preferably rolled or ground. To facilitate proper adhesion of Thyro L to the ration, slightly