Can medicines cause constipation?

How to treat constipation caused by your medications

Easy-to-read information about medicines that commonly cause constipation, who is most at risk and how to treat constipation caused by your medications.

Key points

  1. Some medicines can cause constipation, making you go to the toilet less often than usual to empty your bowels (poo) or pass hard, painful poos.
  2. Medicines known to cause constipation include clozapine, opioids (morphine, codeine, oxycodone, tramadol) and iron tablets.  
  3. If constipation it is not treated it can cause tummy pain, cramping and bloating or serious, life-threatening gut problems that need to be treated as an emergency in hospital. 
  4. Talk to your doctor, nurse or pharmacist if you are concerned that your medicine is making you constipated.

Is my medicine causing constipation?

Because not all constipation is caused by medication, working out whether your symptoms are caused by your medicine is not always easy. If you had a change in bowel movements when you began a new medicine or increased the dose of a medicine you were already taking, it could be because of your medicine. Symptoms of constipation include:

  • passing hard, dry poos
  • not getting the urge to go as often as before
  • having to push really hard when you go
  • feeling like you don't get everything out.

Medicines that commonly cause constipation

Medicines can cause constipation in different ways, such as by affecting the muscles in your gut, affecting your nervous system, which in turn affects your gut muscles, or by causing dehydration. The following are examples of medicines that can cause constipation, especially if taken in higher doses.   

 Examples of medicines that commonly cause constipation 
  • Pain medications such opioids (codeine, morphine, tramadol, oxycodone) or amitriptyline – if you have these medicines regularly you will need to take a laxative. Talk to your doctor or pharmacist.
  • Clozapine – constipation is a very common side effect of clozapine (up to 6 in every 10 people taking clozapine may experience constipation). If not treated, it can lead to serious problems. Let your doctor know if you have stomach pain or feel unwell – you may have constipation that needs to be treated immediately. Read more about clozapine.
  • Iron tablets such as Ferro-Tab®, Ferro-F Tab®, Ferrograd and Ferro-Gradumet®.
  • SSRIs such as fluoxetine and citalopram.
  • Calcium channel blockers such as diltiazem and verapamil.
  • Medicines for urinary incontinence such as oxybutynin.

Note: This is not a complete list. If you have constipation or are unsure whether the medicine you are taking can cause constipation, ask your doctor or pharmacist for advice.

Over-the-counter products such as antacids, antihistamines and paracetamol can cause constipation. Complementary and alternative medicines may also cause constipation. Combinations of any of the above medicines can increase your risk of constipation.

Using too many laxatives

Using too many laxatives and enemas can cause 'rebound' constipation. If you use laxatives too often, your body may rely on them to pass poos. Heavy use of laxatives can also cause runny poos. For the same reason, if you use enemas too often, your body may begin to depend on them. Too many enemas may stop you from having normal bowel movements. Read more about laxatives

Who is most at risk?

You are at increased risk of being constipated if you take any of the medicines listed above. You may be at greater risk of being constipated if you also have a low-fibre diet, aren't getting enough regular exercise or have an illness that affect your nervous system, such as Parkinson's disease, stroke or dementia. Some medical conditions such as diabetes and hypothyroidism (low thyroid) can increase your risk of constipation. 

Constipation is more common in older people mainly because they are often taking lots of medicines, are more likely to be dehydrated, have less exercise and may not have enough fibre in their diet.

If you are in hospital or have just been in hospital

If you are in hospital or have just been in hospital you are at risk of constipation due to changes in diet and less exercise, and you may have started or been given new medicines. If you have just had surgery, it may take a few days for your bowel movements to return to normal.

If you notice changes in your bowel movements while you are in hospital, talk to your nurse or doctor. If you have problems after you go home, talk to your doctor or pharmacist.

What should I do if I think my medicine is causing constipation?

It is important to treat constipation. If it is not treated it can cause tummy pain, cramping and bloating. Straining when passing poos can cause haemorrhoids, anal fissures (tears) and bleeding. In severe cases, constipation can cause faecal impaction and serious, life-threatening gut problems that need to be treated as an emergency in hospital. Here are some ways you can prevent and treat constipation.       

Add foods with more fibre to your diet

At breakfast, high-fibre options include porridge, muesli, bran, wheatgerm, nuts and seeds. Many fruits and vegetables are also high in fibre, especially if the skin is left on. Wholegrain versions of breads, cereals, rice and pasta are best. Adding chickpeas, kidney beans or lentils is a good way to increase fibre in your meals. When baking, white flour can often be mixed with wholemeal flour. 

Fruits and juices high in sorbitol (a type of sugar) can help with constipation. These include apples, apricots, grapes and raisins, peaches, pears, plums and prunes, raspberries and strawberries. Kiwifruit may also improve the symptoms of constipation.

Make sure you drink enough water

Aim for a fluid intake of at least 1.5–2 litres (6–8 glasses) per day. If you have heart failure or advanced chronic kidney disease check with your doctor about how much fluid you can have. 

Keep active and exercise regularly

Being active and doing exercise helps to stimulate the natural movement of your gut muscles that move stools out.

Talk to your doctor or pharmacist if you are concerned

Some people find it difficult to talk about constipation with their doctor or pharmacist. However, they are used to talking about bowel movements, so it's okay to ask, 'could the medicine I am taking cause constipation?' They will check your medicines and may recommend that you use a laxative to ease your symptoms or try a different medicine.

Learn more

Constipation

References

  1. Managing constipation in older people BPAC, NZ, 2019
  2. Clozapine: fatal 'constipation' more common than fatal agranulocytosis Medsafe, NZ, 2007
Credits: Sandra Ponen, Pharmacist. Reviewed By: Angela Lambie, Pharmacist, Auckland Last reviewed: 27 Feb 2020