Q: What are the two types of constipation and what are their causes?

A: Simple (functional): constipation with no underlying pathology

Various causes, but often due to insufficient fluid or fibre in the diet, or reduced mobility. Simple constipation can usually be corrected with dietary or lifestyle measures or short-term use of laxatives. Several drugs also cause constipation.

Drugs with antimuscarinic actions, including:

• Older antidepressants, such as the tricyclics amitriptyline and imipramine
• Antiparkinsonian drugs, eg, orphenadrine, procyclidine and trihexphenidyl
• Antipsychotics, such as chlorpromazine and other phenothiazines.

Others, including:

• Opioid analgesics (morphine, codeine, dihydrocodeine)
• Aluminium-containing antacids
• Antihypertensives (such as verapamil)
• Iron.

Secondary: constipation with an underlying pathological cause

This requires referral for medical investigation. Causes include:

• Bowel obstruction
• Carcinoma
• Faecal impaction
• Irritable bowel syndrome
• Hypothyroidism.