Senna

How it works

Its anthraquinone glycosides are activated by colonic bacteria to stimulate the myenteric plexus, increasing colonic motility and reducing water absorption to promote a bowel movement.

Prescribing in practice

• It should be avoided where intestinal obstruction is suspected, and prolonged use is discouraged; it may be used in pregnancy when dietary measures and a bulk-forming laxative have not worked.
• It can cause abdominal cramping and, with overuse, electrolyte disturbance such as hypokalaemia.
• For opioid-induced constipation, a stimulant laxative such as senna is a rational choice, sometimes combined with a stool softener.

Monitoring

Monitoring is clinical, reviewing bowel response and avoiding prolonged unsupervised use that risks electrolyte imbalance.

Counselling the patient

• It usually works overnight, so it is often taken at bedtime.
• Increase fluid and fibre intake alongside the laxative where possible.
• Stop and seek advice if you have severe abdominal pain or no bowel movement despite treatment.

Evidence & guidelines

Stimulant laxatives such as senna are recommended by NICE for short-term and opioid-related constipation when first-line measures fail.