Hello there, Thank you for your question. Glipizide is a medicine which makes your own pancreas to secrete more insulin. Although Glipizide can be taken at any time of the day, usually dosing depends on which time your sugars rise. It is a short acting drug and many times is given multiple times of the day. The reason for Fasting sugars being high can be dawn phenomenon or sometimes Somogyi effect. Dawn phenomenon is because of certain hormones being active in the morning and increased glucose output from the liver. Whereas Somogyi effect is because of low sugars in the middle of the night and compensatory increase in fasting sugars. I would have considered giving you Metformin for controlling fasting blood sugars better if I were to treat you. Do discuss with your diabetologist about this option, as it requires kidney functions to be tested. Milk thistle is a herb and there is no direct evidence of any interaction between glipizide and milk thistle. But then again as there are no studies which have tried to find any interaction I cannot comment on the same. Many people take many herbal preparations with antidiabetic medicines and have no interaction. Hope this helps. Take care.