You can take it with or without food. Senna takes about 8 hours to work. It's usual to take it at bedtime so it works overnight. Drink plenty of fluids (6 to 8 glasses a day) while you're taking senna or your constipation may get worse.
Take senna in the evening. It should only be used for a few days - this is because your bowel can start to rely on this type of laxative to make it work rather than working on its own. If you are still constipated after taking senna for three days, you should make an appointment to speak with your doctor.
