Senna tea begins to take effect within 1-3 hours of ingesting the brew. Every individual is different, in terms of metabolism and other factors, and that may affect how quickly the tea will begin to work. However, provided you didn’t take any other medications and you have a relatively empty stomach, it should take about two hours to feel the impact.
If you want to use senna tea for overall health, start with a mild brew to see what effects it will have on your body. The laxative effect can be rather intense and may affect people with a sensitive stomach. Find a comfortable strength for senna tea based on your own body, and remember this tea should not be taken for an extended period of time.