NIHR Signal Paracetamol is a weak painkiller for regular tension headaches

Published on 13 September 2016

Paracetamol is only slightly more effective than dummy tablets (placebo) at relieving pain in people who experience regular tension-type headaches.

A Cochrane review found that 24 out of 100 people who took paracetamol for regular tension-type headaches were pain free at two hours, compared with 19 out of 100 who took an inactive placebo.

There was no difference in risk of side effects between paracetamol and placebo.

Paracetamol is a cheap drug that is readily available over-the-counter. Because serious side effects are so uncommon and the “placebo effect” is so strong, this drug could be considered as an option for treating regular tension-type headache for people who find that it helps them.

However, clinicians treating regular tension-type headache may consider alternatives and patients should be made aware that sustained use of paracetamol may cause medication overuse headache.

Paracetamol is a weak painkiller for regular tension headaches

Why was this study needed?

Tension-type headache is the most common type of headache, affecting 21% of people worldwide. These headaches are characterised by pressing or tightening pain (non-pulsating) of mild-to-moderate intensity on both sides of the head.

Frequent episodic tension-type headache is diagnosed when the person has between two and 14 headaches a month. People with frequent tension-type headaches may struggle to concentrate and take more time off work.

Sometimes tension-type headaches get better without treatment, but many people take over-the-counter painkillers as a first treatment.

Paracetamol is a readily available and cheap over-the-counter painkiller, with two tablets (1,000 mg) the most common dose. A systematic review was needed to compile the available evidence on the safety and effectiveness of paracetamol for reducing acute pain in tension-type headache.

What did this study do?

This Cochrane systematic review identified 23 randomised controlled trials assessing the effectiveness and safety of paracetamol in 8079 adults with frequent tension-type headache.

Trials had to have compared paracetamol (taken by mouth) with an inactive placebo, although many also compared paracetamol with another active drug. Trials also had to be double blind, with neither participants nor assessors aware of the treatment given.

The main outcome of interest was whether participants were free from pain two hours after taking paracetamol or placebo.

Most trials were at high or unclear risk of bias, largely because of inadequate reporting of outcomes and lack of clarity on how participants were randomised. Most trials were published before 2000, and the countries and settings were not reported.

What did it find?

  • Pooled analysis of eight high quality studies found that a single 1,000 mg dose of paracetamol was slightly more effective at relieving pain than placebo. Paracetamol stopped pain within two hours in 24 in 100 people, whereas placebo stopped pain in 19 in 100 people (relative risk (RR) 1.3 (95% confidence interval [CI] 1.1 to 1.4).
  • This meant that 22 people with tension-type headache would need to be treated with 1,000 mg paracetamol instead of placebo for one person to be pain free at two hours.
  • The broader outcome of being pain free or having only mild pain at two hours was achieved by 59 out of 100 people taking paracetamol compared with 49 out of 100 taking placebo (RR 1.2 (95% CI 1.15 to 1.3).
  • There was no difference between paracetamol or placebo in the number of people experiencing side effects, which affected around 1 in 10 people. Side effects were mostly mild, and no participants had serious side effects.
  • Paracetamol 1,000 mg was about as effective as ibuprofen 400 mg, with 33 in 100 people pain free at two hours with paracetamol and 38 in 100 with ibuprofen. This analysis used three low quality trials and results should be treated cautiously.

What does current guidance say on this issue?

The 2012 NICE guideline on diagnosis and management of headaches (currently being updated) recommends considering aspirin, paracetamol or a non-steroidal anti-inflammatory drug, such as ibuprofen, for acute treatment of tension-type headache. The treatment choice should take into account the person’s preference, other illnesses and risk of adverse events.

The guideline adds that healthcare professionals should be alert to the possibility of medication overuse headache in people whose headache developed or worsened while taking paracetamol on at least 15 days per month over a period of three months or more.

What are the implications?

This review suggests that paracetamol has a minimal effect on relieving pain in people with frequent tension-type headache compared to placebo.

However, the drug is very cheap and available over-the-counter, which is of importance to patients given that many with this type of headache do not seek medical help.

Paracetamol also had a low rate of side effects. Therefore, paracetamol remains an option for people with frequent tension-type headaches who find that it helps.

Citation and Funding

Stephens G, Derry S, Moore RA. Paracetamol (acetaminophen) for acute treatment of episodic tension-type headache in adults. Cochrane Database Syst Rev. 2016;(6):CD011889.

Cochrane UK and the Pain, Palliative and Supportive Care Cochrane Review Group are supported by NIHR infrastructure funding.

Bibliography

NHS Choices. Tension-type headaches. London: Department of Health; 2015.

NICE. Headaches in over 12s: diagnosis and management. CG150. London: National Institute for Health and Care Excellence; 2012.

NICE. Clinical Knowledge Summary. Headache - tension-type. London: National Institute for Health and Care Excellence; 2015.

Why was this study needed?

Tension-type headache is the most common type of headache, affecting 21% of people worldwide. These headaches are characterised by pressing or tightening pain (non-pulsating) of mild-to-moderate intensity on both sides of the head.

Frequent episodic tension-type headache is diagnosed when the person has between two and 14 headaches a month. People with frequent tension-type headaches may struggle to concentrate and take more time off work.

Sometimes tension-type headaches get better without treatment, but many people take over-the-counter painkillers as a first treatment.

Paracetamol is a readily available and cheap over-the-counter painkiller, with two tablets (1,000 mg) the most common dose. A systematic review was needed to compile the available evidence on the safety and effectiveness of paracetamol for reducing acute pain in tension-type headache.

What did this study do?

This Cochrane systematic review identified 23 randomised controlled trials assessing the effectiveness and safety of paracetamol in 8079 adults with frequent tension-type headache.

Trials had to have compared paracetamol (taken by mouth) with an inactive placebo, although many also compared paracetamol with another active drug. Trials also had to be double blind, with neither participants nor assessors aware of the treatment given.

The main outcome of interest was whether participants were free from pain two hours after taking paracetamol or placebo.

Most trials were at high or unclear risk of bias, largely because of inadequate reporting of outcomes and lack of clarity on how participants were randomised. Most trials were published before 2000, and the countries and settings were not reported.

What did it find?

  • Pooled analysis of eight high quality studies found that a single 1,000 mg dose of paracetamol was slightly more effective at relieving pain than placebo. Paracetamol stopped pain within two hours in 24 in 100 people, whereas placebo stopped pain in 19 in 100 people (relative risk (RR) 1.3 (95% confidence interval [CI] 1.1 to 1.4).
  • This meant that 22 people with tension-type headache would need to be treated with 1,000 mg paracetamol instead of placebo for one person to be pain free at two hours.
  • The broader outcome of being pain free or having only mild pain at two hours was achieved by 59 out of 100 people taking paracetamol compared with 49 out of 100 taking placebo (RR 1.2 (95% CI 1.15 to 1.3).
  • There was no difference between paracetamol or placebo in the number of people experiencing side effects, which affected around 1 in 10 people. Side effects were mostly mild, and no participants had serious side effects.
  • Paracetamol 1,000 mg was about as effective as ibuprofen 400 mg, with 33 in 100 people pain free at two hours with paracetamol and 38 in 100 with ibuprofen. This analysis used three low quality trials and results should be treated cautiously.

What does current guidance say on this issue?

The 2012 NICE guideline on diagnosis and management of headaches (currently being updated) recommends considering aspirin, paracetamol or a non-steroidal anti-inflammatory drug, such as ibuprofen, for acute treatment of tension-type headache. The treatment choice should take into account the person’s preference, other illnesses and risk of adverse events.

The guideline adds that healthcare professionals should be alert to the possibility of medication overuse headache in people whose headache developed or worsened while taking paracetamol on at least 15 days per month over a period of three months or more.

What are the implications?

This review suggests that paracetamol has a minimal effect on relieving pain in people with frequent tension-type headache compared to placebo.

However, the drug is very cheap and available over-the-counter, which is of importance to patients given that many with this type of headache do not seek medical help.

Paracetamol also had a low rate of side effects. Therefore, paracetamol remains an option for people with frequent tension-type headaches who find that it helps.

Citation and Funding

Stephens G, Derry S, Moore RA. Paracetamol (acetaminophen) for acute treatment of episodic tension-type headache in adults. Cochrane Database Syst Rev. 2016;(6):CD011889.

Cochrane UK and the Pain, Palliative and Supportive Care Cochrane Review Group are supported by NIHR infrastructure funding.

Bibliography

NHS Choices. Tension-type headaches. London: Department of Health; 2015.

NICE. Headaches in over 12s: diagnosis and management. CG150. London: National Institute for Health and Care Excellence; 2012.

NICE. Clinical Knowledge Summary. Headache - tension-type. London: National Institute for Health and Care Excellence; 2015.

Paracetamol (acetaminophen) for acute treatment of episodic tension-type headache in adults

Published on 17 June 2016

Stephens, G.,Derry, S.,Moore, R. A.

Cochrane Database Syst Rev Volume 6 , 2016

BACKGROUND: Tension-type headache (TTH) affects about 1 person in 5 worldwide. It is divided into infrequent episodic TTH (fewer than one headache per month), frequent episodic TTH (two to 14 headaches per month), and chronic TTH (15 headache days a month or more). Paracetamol (acetaminophen) is one of a number of analgesics suggested for acute treatment of headaches in frequent episodic TTH. OBJECTIVES: To assess the efficacy and safety of paracetamol for the acute treatment of frequent episodic TTH in adults. SEARCH METHODS: We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (CRSO), MEDLINE, EMBASE, and the Oxford Pain Relief Database to October 2015, and also reference lists of relevant published studies and reviews. We sought unpublished studies by asking personal contacts and searching online clinical trial registers and manufacturers' websites. SELECTION CRITERIA: We included randomised, double-blind, placebo-controlled studies (parallel-group or cross-over) using oral paracetamol for symptomatic relief of an acute episode of TTH. Studies had to be prospective, with participants aged 18 years or over, and include at least 10 participants per treatment arm. DATA COLLECTION AND ANALYSIS: Two review authors independently assessed studies for inclusion and extracted data. We used the numbers of participants achieving each outcome to calculate the risk ratio (RR) and number needed to treat for one additional beneficial outcome (NNT) or one additional harmful outcome (NNH) for oral paracetamol compared to placebo or an active intervention for a range of outcomes, predominantly those recommended by the International Headache Society (IHS).We assessed the evidence using GRADE (Grading of Recommendations Assessment, Development and Evaluation) and created 'Summary of findings' tables. MAIN RESULTS: We included 23 studies, all of which enrolled adults with frequent episodic TTH. Twelve studies used the IHS diagnostic criteria or similar, six used the older classification of the Ad Hoc Committee, and five did not describe specific diagnostic criteria but generally excluded participants with migraines. Participants had moderate or severe pain at the start of treatment. While 8079 people with TTH participated in these studies, the numbers available for any analysis were lower than this because outcomes were inconsistently reported and because many participants received active comparators.None of the included studies were at low risk of bias across all domains considered, although for most studies and domains this was likely to be due to inadequate reporting rather than poor methods. We judged five studies to be at high risk of bias for incomplete outcome reporting, and seven due to small size.For the IHS preferred outcome of being pain free at two hours the NNT for paracetamol 1000 mg compared with placebo was 22 (95% confidence interval (CI) 15 to 40) in eight studies (5890 participants; high quality evidence), with no significant difference from placebo at one hour. The NNT was 10 (7.9 to 14) for pain-free or mild pain at two hours in five studies (5238 participants; high quality evidence). The use of rescue medication was lower with paracetamol 1000 mg than with placebo, with an NNTp to prevent an event of 7.8 (6.0 to 11) in six studies (1856 participants; moderate quality evidence). On limited data, the efficacy of paracetamol 500 mg to 650 mg was not superior to placebo, and paracetamol 1000 mg was not different from either ketoprofen 25 mg or ibuprofen 400 mg (low quality evidence).Adverse events were not different between paracetamol 1000 mg and placebo (RR 1.1 (0.94 to 1.3); 5605 participants; 11 studies; high quality evidence). Studies reported no serious adverse events.The quality of the evidence using GRADE comparing paracetamol 1000 mg with placebo was moderate to high. Where evidence was downgraded it was because a minority of studies reported the outcome. For comparisons of paracetamol 500 mg to 650 mg with placebo, and of paracetamol 1000 mg with active comparators, we downgraded the evidence to low quality or very low quality because of the small number of studies and events. AUTHORS' CONCLUSIONS: Paracetamol 1000 mg provided a small benefit in terms of being pain free at two hours for people with frequent episodic TTH who have an acute headache of moderate or severe intensity.

Tension-type headache is a common, mild and self-limiting type of headache. It can be divided into three types: infrequent episodic (less than one headache per month), frequent episodic (two to 14 headaches per month) and chronic (15 headache days a month or more).

The International Headache Society recommends that controlled trials of drugs in tension-type headache should use a pain-free rate at two hours as the main outcome measure. Only eight of the 23 studies included in this Cochrane review reported this recommended outcome. The other studies reporting pain relief at other time points, such as one hour or four hours after dosing, or reduction in pain.

Expert commentary

The data suggests that paracetamol is relatively ineffective for frequent episodic tension-type headache. We do not know how well it might work for infrequent headaches, or whether some people might consistently respond to treatment. Regular use of paracetamol can lead to medication overuse headache. Perhaps we need to advise no more than very occasional use of paracetamol for headaches, and only then if the patient consistently experiences benefit.

Professor Martin Underwood, Director, Warwick Clinical Trials Unit, Warwick Medical School, The University of Warwick

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