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Body clocks and medicines
Almost every cell in your body keeps time. These daily rhythms affect how medicines are absorbed, how strongly they act, and how quickly they leave your body.
What is chronopharmacology?
Chronopharmacology is the study of how the time of day changes the effects of medicines. Your brain's master clock — the suprachiasmatic nucleus — is reset each morning by light. It keeps "peripheral clocks" in the liver, gut, kidneys and immune cells in sync. Because these organs process drugs, the same dose can behave differently at 08:00 and 20:00.
A day in your body
Typical timings for someone who sleeps from about 23:00 to 07:00. Your own rhythm may run earlier or later.
- 100:00 Liver cholesterol synthesis peaks (overnight)
- 202:00 Deepest sleep
- 304:00 Asthma symptoms & airway narrowing worst
- 404:30 Lowest body temperature
- 506:45 Sharpest blood pressure rise
- 607:30 Melatonin secretion stops
- 708:00 Cortisol peaks · heart attacks most common (06–12)
- 810:00 Highest alertness
- 914:30 Best coordination
- 1017:00 Greatest muscle strength & cardiovascular efficiency
- 1118:30 Highest blood pressure
- 1219:00 Highest body temperature
- 1321:00 Melatonin secretion starts
- 1422:00 Stomach acid secretion peaks
How timing changes a medicine
Doctors describe what the body does to a drug in four steps. Each one has a daily rhythm.
Absorption
Stomach acid, gut blood flow and how fast the stomach empties all change across the day. Many tablets are absorbed faster in the morning.
Distribution
Blood flow to organs and the proteins that carry drugs in the blood rise and fall daily, changing where a medicine goes.
Metabolism
Liver enzymes (such as the CYP family) that break down drugs follow clock genes, so the same dose can be cleared faster at one time than another.
Excretion
Kidney filtration is highest during the day and lowest at night, affecting how quickly medicines leave the body.
The target matters too: symptoms of many illnesses follow the clock. Asthma is worst around 04:00, rheumatoid arthritis stiffness on waking, and heart attacks are most common in the morning.
Reading the clocks on this site
- Noon is at the top, midnight at the bottom. Time moves clockwise.
- The lighter top half is daytime; the blue-grey bottom half is night.
- The solid teal band shows the best window to take the medicine.
- A dotted ring means any time is fine — just be consistent.
Evidence levels
Consistent clinical trials or official prescribing guidance support this timing.
Supported by studies and drug pharmacology, but guidance varies between sources.
Promising early or observational research — not yet standard practice everywhere.
Studies disagree. Taking it at the same time every day matters more than the hour.