Variations & Complications

A mother playing with her child

Below we explain the differences between developmental and acquired, as well as overt and covert stammering — and set out some of the conditions which may co-exist with a stammer.

Developmental & Acquired

Developmental Stammering

Most people who stammer start doing so in early childhood when they’re learning to speak. This is known as 'developmental stammering'. Up to 8% of children will experience stammering at some point. For most children, stammering will resolve over time, either naturally or with support from speech and language therapy. Around 2% of adults stammer in the UK.

Acquired Stammering

Stammering which starts later in life, known as 'acquired', 'late onset' or 'adult onset' stammering, is much less common. There are several types of acquired stammering, which are listed below.

Types of acquired stammering

1. Neurogenic stammering

This is the most common type of acquired stammering. It's caused by some kind of brain trauma, such as:

  • a stroke (the most common cause),
  • a head injury
  • a brain tumour
  • it can also be associated with Parkinson's disease and some forms of dementia.

2. Drug-related stammering

Stammering can sometimes occur as a side effect while taking medication or other drugs. If you're taking a prescribed medicine and you experience any sort of speech problem, consult your doctor immediately. They may be able to prescribe a different medicine, or they may adjust the dosage to lessen the side effects. 

Drug-related stammering will almost certainly disappear completely if you stop using the drug. However, it can be dangerous to stop taking medication, either due to the way the body reacts to withdrawal of medication or because of the loss of the associated health benefits. So please seek medical advice before considering any changes to your medication.

3. Psychogenic stammering

A stressful event, or prolonged, intense stress over time can sometimes result in stammering. This is known as 'psychogenic stammering'.

Common sources of stress include a major bereavement or loss of a relationship. A reaction to stress can also follow after an accident, for example a car crash. However, in this sort of situation it’s not always easy to work out if the stammer is stress-related or has a neurogenic cause, for example a head injury which may have gone undiagnosed (see above for neurogenic stammering).

Speaking had been my strength and now suddenly all the words were trapped inside my head and unable to come out.

Read Hannah's experience of starting to stammer later in life.

Psychogenic stammering is likely to reduce when the event or situation causes you less stress or anxiety. Counselling can be helpful in dealing with stress and anxiety, along with support from a speech & language therapist to address concerns around the stammering itself. Sometimes stress-related stammering does not disappear once the cause of stress has been removed or overcome. In any case, it’s best to get help from a speech & language therapist (see 'Getting Help' below). Find out about NHS counselling services.

The NHS provides psychological therapies for people experiencing stress or anxiety. Contact your GP for details. If you live in England, you can refer yourself to a psychological therapies service without seeing your GP — see the NHS website for more details. 

Here are links to some other organisations that offer counselling services: 

  • Samaritans  talk to someone if something's troubling you.
  • Cruse — for bereavement advice and support.
  • Relate — for relationship advice and counselling.
  • Rape Crisis England & Wales — for women and girls who have been raped or sexually abused.
  • Victim Support — for victims or witnesses of crime.

4. Re-occurrence of a childhood stammer

Some people start stammering in early childhood, then stop stammering as they grow up, and find it re-occurs at some point in their adult life.  This is a complex area for several reasons. Firstly, you may have gone through a period of stammering when you were very young but don't remember it.  

Secondly, stammering can sometimes be almost completely covert or hidden. From an early age, some people who stammer cope by avoiding particular words or sounds that cause them difficulty, or by avoiding certain speaking situations — so any stammering is barely noticeable (see 'Overt vs Covert Stammering' below). These habits can become so ingrained that you stop seeing yourself as someone who stammers. But these ways of coping can sometimes break down without warning, perhaps as a result of added pressure in your life, for instance.

If a childhood stammer re-occurs, it's worth trying speech & language therapy. It has helped many adults significantly, even if it didn't help when they were younger. Therapy has changed a lot over the years — and you may have too.

5. Individual causes of stammering

Sometimes it may not be possible to find out what's caused acquired stammering. If no cause can be identified, and it doesn't fit any of the above categories, it may be what's called 'idiopathic stammering'. This term means it relates purely to the person concerned and does not fall into any of the above categories.

Getting help

If you start stammering as an adult, speak to your doctor. They might refer you to a specialist consultant or to a speech & language therapist. Many of the speech therapy approaches used for people with a developmental stammer (see above) will also be helpful to those with an acquired stammer.

You can also refer yourself for speech & language therapy – see our Therapy & Courses section or call the STAMMA helpline on 0808 802 0002 and we’ll help (open weekdays 10am-12pm and 6pm-8pm). If you can afford it, you can also see a private speech and language therapist — contact the Association of Speech and Language Therapists in Independent Practice.

Meeting other people who stammer is a good way of getting support. You can join the Adults New to Stammering group that meets online. Or, see if there's a general stammering group near you by going to our Local Groups page.

Overt & Covert Stammering

Overt stammering is what you hear when people stammer. Most people who stammer will find ways to hide their stammer, to make their stammer less obvious. Someone who has a covert stammer, also known as an 'interiorised' or 'hidden' stammer, will appear not to stammer at all, or only stammer very occasionally. Typically, they will have:

  • high levels of fluency
  • high levels of avoidance, for example changing words or saying less
  • strong negative feelings about stammering.

Someone with an interiorised stammer will often:

  • hide the fact that they stammer
  • worry that people will find out they stammer
  • have few people in their life that know they stammer
  • feel ashamed of their 'secret' stammer 
  • search ahead in their mind for potentially difficult sounds
  • substitute feared words for others that are easier to say
  • use complex avoidance strategies to hide their stammer.

People whose stammering is more noticeable might also do these things; the difference is that someone with a covert stammer will appear largely fluent. While they may not be seen to stammer, emotionally and internally this will be something very much on their minds. It's the emotional side of things that's key here: the negative thoughts, feelings and constant avoidance to hide the stammer.

If you have a covert stammer, it can be hard for other people to understand how it makes you feel. People will reassure you that they never knew you stammered, so it can't be that bad. This can leave you feeling like you're making an unnecessary fuss. 

In extreme cases you may have been so 'successful' in your hiding it, that in fact you are not believed for having a stammer at all. This can be very frustrating and painful, as it effectively denies you have a problem. Just because your stammer is hidden it is not less of a problem, it's a different sort of problem.

If you have a covert stammer, then speech and language therapy can be liberating. Speech & language therapists know how strong the feelings associated with hiding a stammer can be, and the impact it can have on your life. See our Therapy & Courses section.


Someone who clutters has a very fast rate of speech, and talks in rapid bursts, making them hard to understand. This is closely related to stammering. People who clutter may:

  • leave off word endings
  • omit or distort sounds or syllables ('elephant' becomes 'elphant'; 'orange' becomes 'orng')
  • run their words together
  • use lots of fillers words, like 'as', 'um' or 'uh'
  • repeat or revise phrases, or words 
  • have difficulty organising thoughts or getting to the point
  • find it hard to slow down, even when asked
  • tend to interrupt.

Cluttering often exists alongside other speech differences, including stammering. Cluttering can also occur alongside attention deficit hyperactivity disorders (ADHD) or autistic spectrum disorder (ASD).

A person who clutters may be unaware of any difficulty, so a parent, manager or colleague may suggest that they get help because they find it hard to understand them.

Help with cluttering

Speech & language therapists who specialise in stammering are also trained in supporting people who clutter. So, if you or your child clutters, contact your local NHS speech & language therapy service (see our Therapy & Courses section). Paying for private therapy is another option. Go to the Association of Speech and Language Therapists in Independent Practice website to find something near you. City Lit, an adult education centre in London, sometimes offers courses for people who clutter.

Therapy will vary from person to person. Becoming more aware of when they aren't being understood can help someone who clutters. They can then use strategies like pausing between phrases and sentences and over-articulating certain words to make themselves understood.

Sources of information & support

Cluttering (Stuttering Foundation of America) — useful guidelines for identifying cluttered speech and ideas for managing it, from the Stuttering Foundation of America. 

International Cluttering Association — a membership organisation (free to join) open to people who clutter and Speech and Language Therapists with lots of helpful information and advice.

First Online Cluttering Conference — from May 2010 is still accessible online.


The City Lit adult education centre in London runs courses for people who clutter. See the City Lit's website for more details.

Stammering & Down's Syndrome

Stammering is common in people with Down's syndrome, who will often have other speech and language problems and hearing loss. This means someone with Down’s can be hard to understand. Down's syndrome may also cause learning difficulties, which can affect the ability to understand and produce speech.

Someone with Down’s syndrome might:

  • repeat whole words or parts of words while trying to think of the next bit of the sentence ("it's…it's…it's…big.")
  • have long pauses in the middle of the sentence when they can’t think of what to say next ("it's a…ball.")
  • pause in unusual places in sentences, often followed by two or three words in a sudden rush that may be hard to understand ("I'm going swim…mint'morrow.")
  • stress the wrong word in a sentence or on the wrong part of the word
  • struggle to find the right speech sound to start the word off.

When talking with someone with Down’s syndrome, you can help by:

  • giving them plenty of time to speak and plan what they want to say
  • pause before responding or talking, and slow the conversation down
  • avoid finishing sentences or saying what you think they're trying to say
  • if you haven’t understood what they said, ask them to repeat it. It’s best to be honest
  • avoid long or complicated sentences
  • give positive encouragement for the message rather than the style of delivery
  • use gestures to illustrate your conversation. 

Let them know you value what they are saying and want to hear them.

sources of information & support

The Down's Syndrome Association

For Families and Carers: Communication series — practical tips and activities from the Down's Syndrome Association, for supporting children and young people to develop their communication skills. 


Exploring Fluency in Down's Syndrome – a discussion of speech dysfluencies for professionals and parents by Monica Bray (2016).

Stammering & autism

Dysfluencies in the speech of those on the autistic spectrum are common. Autism affects the way people experience the world around them and the way they communicate. Every person with autism is different — some people may talk very little, while others may talk a lot and be very fluent. Some people may be very aware of their dysfluencies and may develop negative thoughts and feelings about their speech, while others may have little or no awareness that their speech patterns are disrupted.

The range of dysfluencies can be quite broad, and includes features such as:

  • Stammering – this includes sound prolongations, repetitions or blocks, particularly at the beginning of words, that are familiar to many people who stammer.
  • The normal dysfluencies present in everyone’s speech, but at a higher rate than is typical. This includes 'um's and 'er's, hesitations, rephrasing and pauses.
  • Less common dysfluencies. This includes features such as repetition of sounds at the end of words, repetition of words at the end of a phrase or sentence, or inserting extra sounds in the middle of words.

How to help someone with autism:

•    Give them time to plan what they want to say.

•    Say exactly what you mean. Don't use slang, sarcasm or idioms such as "she’s as cool as a cucumber" or "it went down to the wire". Taken literally this can be hard for some people with autism spectrum conditions to understand.

•    Eye contact can be very uncomfortable for some people with autism spectrum conditions, so don’t be offended if the person doesn’t make eye contact during a conversation.

Sources of support & information

National Autistic Society, which has some useful communication tips

The autism pages on the NHS website.

Tourette's Syndrome

Tourette's Syndrome (TS) is thought to affect about one per cent of the population, affecting all races and ethnic groups equally. It typically starts around the age of 6, with very few children developing TS beyond the age of 13. In up to 70% of children with TS, the tics will significantly reduce or diminish by late adolescence.  

Tourette's Syndrome and stammering share many characteristics. They are both neurological conditions — that is the cause for both lies within the brain. Both have a strong genetic component and both affect more boys than girls.  

The main signs of TS are involuntary sounds and movements. This includes unintentional repeated movements, such as shoulder shrugs, eye-blinking or head twitches and repeated sounds such a throat clearing, sniffing, making a specific noise or repeating words or phrases.

Saying rude words or swearing is probably the best-known sign of TS, but this only affects a small number of children.

Like stammering, no two people with TS display precisely the same tic characteristics.

TS can be managed with medication, behavioural management and counselling support. Sometimes the vocal tics of children with TS may resemble stammering behaviours. If you think your child may be stammering and would like support with this, ask your GP or refer yourself to your local NHS Speech & Language Therapist (see our Therapy & Courses section). If possible, see someone who specialises in working with children who stammer.

Sources of Support & Information

Tourette's Action (Helpline: 0300 777 8427)

Tic Disorders: A Guide for Parents and Professionals — a book by Uttom Chowdhury and Tara Murphy (2016), Jessica Kingsley Publishers.