Blisters on the tongue can have one of several different causes. Most likely drinking coffee won't make then any better or any worse. I think the most important next step is to get to the bottom of your tongue blisters. I think they could be one of several things. They could be an allergic reaction to some food you are eating (likely not coffee) or a new drug you are taking. Another likely possibility is cold sores (oral Herpes). This is a viral infection that will appear to come and go usually during times of stress or being run down. As far as your coffee consumption goes, just drink it in moderation. One or two cups in the morning is probably not going to do a lot of harm. Total caffeine consumption is what you want to keep down, so stay away from the energy drinks, especially in the afternoon. I suggest that you schedule an appointment with your primary care physician
, especially when you develop the blisters. If they are treatable, and they bother you, then getting to the bottom of it will be a good thing. Remember, take it easy on the coffee, and no energy drinks. Good luck.