Senokot’s own label says to “take preferably at bedtime,” and the reason is straightforward: the medication takes roughly 6 to 12 hours to work. Taking it before you go to sleep means the effect arrives in the morning, when you’re awake, upright, and near a bathroom. That timing also lines up with your body’s natural morning signals to move your bowels.
How Nighttime Dosing Lines Up With Morning
Senna, the active ingredient in Senokot, stimulates the muscles of your colon to push waste along. That process isn’t instant. The NHS puts the average onset at about 8 hours, while the broader range for stimulant laxatives is 6 to 12 hours. If you take your dose at 10 p.m., you can expect results somewhere between 4 a.m. and 10 a.m., with the sweet spot for most people landing right around breakfast time.
This matters because your digestive system is already geared up for a bowel movement in the morning. When you eat breakfast, your stomach stretches to make room, and nerves automatically signal your colon to start clearing space. This is called the gastrocolic reflex, and it triggers large, wave-like contractions that push stool toward the exit. Senokot’s effect stacks on top of that natural reflex, making the morning the most effective window for a comfortable, predictable result.
Why Daytime Dosing Is Less Practical
If you took Senokot first thing in the morning instead, the urge to go would hit somewhere in the afternoon or evening. That could mean dealing with cramping or urgency during work, errands, or social situations. Stimulant laxatives can also cause loose stools, and having that happen unpredictably during the day is something most people would rather avoid. You’re also asleep for the hours when the medication is building up its effect, which means you skip the waiting period entirely and wake up when results are close.
Standard Dosing for Adults and Children
For adults and children 12 and older, the starting dose is 2 tablets once a day at bedtime. If that isn’t enough, the maximum is 4 tablets twice a day, though most people find relief at a lower dose. Children aged 6 to 11 start with 1 tablet, and children aged 2 to 5 start with half a tablet. For children under 2, a doctor should decide.
Senokot is meant for short-term, occasional constipation. The UK’s medicines regulator limits over-the-counter pack sizes to reflect this: enough for two short courses, not ongoing daily use. If you find yourself reaching for it regularly, that’s a sign to look at dietary changes first (more fiber, more water, more movement) or talk to a healthcare provider about what’s behind the constipation.
Common Side Effects
Stomach cramps and diarrhea are the most common side effects, occurring in more than 1 in 100 people. If you have constipation related to IBS, you’re more likely to experience both. One harmless quirk: senna can turn your urine a red-brown color. It looks alarming but goes away once you stop taking it.
Taking Senokot at bedtime has a practical benefit here too. Mild cramping is easier to sleep through than to deal with during the day, and by the time you’re awake, the initial discomfort has often passed.
When Senokot Isn’t the Right Choice
Senna should be avoided if you have severe stomach pain with nausea or vomiting, a suspected bowel blockage, or an acute abdominal condition like appendicitis. People with Crohn’s disease, ulcerative colitis, kidney problems, or heart problems should check with a doctor before using it. The same goes if you’re pregnant, breastfeeding, or trying to conceive. Signs of dehydration (peeing less than usual, dark or strong-smelling urine) are also a reason to hold off, since stimulant laxatives can worsen fluid loss.