Yes, in most cases you can drink plain, unsweetened herbal tea while fasting.

Key point

For intermittent fasting or other health-related fasts, calorie‑free drinks like water and unsweetened herbal tea (no sugar, honey, milk, or fruit pieces) are usually considered fine and do not meaningfully affect blood sugar or insulin. This means they are unlikely to “break” a standard intermittent fast. However, if the fast is religious (like Ramadan during the day, or other traditions that forbid all drinks), then even herbal tea would not be allowed, so you must follow the specific rules of that fast. If you are unsure or have medical conditions, it is safest to ask a healthcare professional or religious authority which drinks are permitted for your specific type of fasting.