Yes, your meal plans may need to be adjusted on the days you work out. That's because exercise affects the way your body regulates insulin and other hormones, which in turn will affect how many carbs and how much medication you need to keep your blood sugar in a healthy zone. A nice bonus: Over the long run, physical activity improves insulin sensitivity, meaning you need less insulin to drive sugar into the body's cells, which can have the happy side effect of lowering your medication doses.
On some medications, exercise can cause blood sugar to drop. During exercise, your muscles require a lot of glucose to fuel your workout. To help get more glucose into the muscles, muscle cells temporarily become more insulin sensitive. So if you take insulin or a drug that stimulates your own insulin production, your regular dose may be too high, driving too much blood sugar into the muscles and leaving too little in the bloodstream. The result: Blood sugar drops, maybe a little, maybe to hypoglycemic levels. Chances are you'll need a lower dose before exercising—but don't make any adjustments without checking with your doctor.
Another reason blood sugar could drop during exercise is because you're not producing enough adrenaline, which is a problem for people with autonomic neuropathy—a common complication of diabetes.