Variations & Complications

Mother playing with a child who has Downs Syndrome

Below we describe the main aspects of stammering: developmental versus acquired, and overt versus covert – and set out some of the conditions which may co-exist with a stammer.

We also have information leaflets for parents, children, young people and adults which you can read and share with others. Download them here or order physical copies for free here.

Developmental & Acquired

Developmental Stammering

Most people who stammer start stammering when learning to speak. This is known as ‘developmental stammering’. Up to 8% of children will experience this, and the majority will stop stammering, either spontaneously or through speech therapy. Those who continue to stammer will do so (to differing degrees) throughout adulthood.

Acquired Stammering

Less common is ‘acquired stammering’ (also known as ‘late onset stammering’), which starts later in life. If you start stammering in adulthood, take it seriously and consult your doctor as soon as you can. Your doctor might refer you on to a specialist consultant or a speech and language therapist, or you can refer yourself to a NHS therapist. See our page called 'Finding a NHS therapist'.

Types of acquired stammering

Below are the main types of acquired stammering.

1. Neurogenic stammering

Neurogenic stammering is the most common type of acquired stammering. It is caused by some kind of brain trauma such as a stroke, head injury or brain tumour. Other causes include Alzheimer’s disease and Parkinson’s disease.  

Having a stroke is the most frequent cause of neurogenic stammering – a stroke is a blood clot or bleeding in the brain, resulting in damage to a specific part of the brain. Stammering is one of several different speech problems which can occur as a result of a stroke or brain injury. Speech problems associated with a stroke may only last a few hours, but they should not be ignored, so seek medical advice immediately.

Check out Stroke Association’s website for information about communication problems after a stroke and about speech and language therapy for stroke patients.

2. Drug-related stammering

Stammering can sometimes occur as part of an adverse reaction or side-effect whilst taking medication or other drugs. If you are taking a prescribed medicine and find you are affected by any sort of speech problem, consult your doctor immediately. They may be able to prescribe an alternative medicine or adjust the dosage so that side-effects are minimised. 

Drug-related stammering will almost certainly disappear completely if you stop using the drug but this might not always be an option.

3. Psychogenic stammering

A stressful event, or a series of events that affects you psychologically, 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. 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).

Psychogenic stammering is likely to improve when the event or situation no longer causes you stress or anxiety. Some sources of stress, such as a bereavement, may be long-lasting and in these situations counselling can help. Cruse is a national charity offering counselling to the bereaved. Visit the Cruse website here.

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 and language therapist.

4. Re-occurrence of a childhood stammer

Some people start stammering in early childhood then stop as they grow up, but find it re-occurs at some point in adulthood. 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. Some people who stammer cope with it by avoiding particular words, sounds or speaking situations from an early age so that hardly any stammering is noticeable (see our information on covert stammering below). These habits can become so ingrained that you no longer think of yourself as someone who stammers. However, these ways of coping can sometimes break down without warning, perhaps as a result of added pressure in your life, or for reasons which can't be explained.

If a childhood stammer re-occurs and you would like to do something about it, try speech and language therapy. Even if you had speech and language therapy when you were younger but it didn't help, it is worth trying again because you may have changed and therapy has certainly changed.

5. Individual causes of stammering

Sometimes it may not be possible to find out what has caused acquired stammering. When no cause is identified, this is known as as ‘idiopathic stammering’, which 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 and would like to get help, start by going to your GP. It is also useful to see a speech and language therapist. In most parts of the UK you can refer yourself directly to your local NHS speech and language therapy department. Search online for ‘adult speech and language therapy + your location’ or call the Stamma helpline on 0808 802 0002 and we’ll help. 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. See if there is a 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 and Language Therapists know how strong the feelings associated with hiding a stammer can be, and the impact it can have on your life.  


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.

Speech and Language Therapists who specialise in stammering are also trained in supporting people who clutter, so if you have a clutter, or someone you know does, then contact the local NHS speech and language therapy service. 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.

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 and Language Therapist. 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.

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