Can you take 1 mg of melatonin if you have a thyroid condition? And what effect does it have on it

0.3 - 1.0 mg. Take it 90min before sleep. Take the smaller dose and see if it works. Much higher doses can actually interfere with sleep. If you have a "thyroid" condition, it should be evaluated an treated properly asap. Also, your herbs and supplements can interfere with medication, have adverse side effects, and don't help you in any way. Don't believe what you read on the internet or hear from friends.
Melatonin. Some studies show that melatonin can affect thyroid function (possibly inhibiting its activity), but these are far from definitive.Current recommendations are that it can be used cautiously. http://www.ncbi.nlm.nih.gov/pubmed/12019356?dopt=abstract please discuss with your physician in detail. The 1mg dose is less than the 3mg and higher doses often available, and would be safer if concerned.