It's not considered to be incompatible in a dangerous sense, but Co-Q 10 supplements have been shown to decrease the effectiveness of coumadin. If you decided to add this supplement to your regime, it may thus be necessary to increase your dose of coumadin in order to maintain your level of treatment. No other interactions are indicated between co q10 and the other medications you mentioned: lipitor and levoxyl.
You can find more information about the properties, dose, and effects of coenzyme-q 10 here: http://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/coe_0084.shtml
I hope this helps! Let me know if you have any further questions.
Biologist
Expertise in Reproductive/Sexual Health, Psychology, Substance Abuse, General Medicine, Pharmacology