This is a good question to ask. We have a lot of data on Alli (orlistat) because it is a lower dose of a prescription medication. You can take Alli while on Synthroid, but you want to space the medications by four hours, so take your Synthroid at 8 a.m. on an empty stomach, and you can then take Alli at noon. You also want to let your doctors and health care providers know that you are taking Alli and include it on your personal medication list.
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