Acetaminophen 1000mg demonstrated a small benefit in regards to being pain-free at 2 hours for patients with frequent tension-type headache (TTH) who have an acute headache of moderate or severe intensity, study authors reported in a Cochrane review.

Acetaminophen is a common analgesic recommended for acute treatment of headaches in patients with frequent episodic TTH. Researchers from the University of Oxford aimed to asses the safety and efficacy of  acetaminophen in these patients. They started by searching the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, and the Oxford Pain Relief Database to October 2015 for randomized, double-blind, placebo-controlled studies that used oral acetaminophen for symptomatic relief of an acute episode of TTH.

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A total of 23 studies, which included 8,079 adults with frequent episodic TTH, were included; all patients had moderate or severe pain at the start of treatment. 

For the International Headache Society (IHS) preferred outcome of being pain-free at 2 hours, the number needed to treat (NNT) for acetaminophen 1000mg vs. placebo was 22 (95% CI: 15–40) in 8 studies (high quality evidence) with no significant difference from placebo at 1 hour. The NNT was 10 (95% CI: 7.9–14) for pain-free or mild pain at 2 hours in 5 studies (high quality evidence). 

Patients treated with acetaminophen 1000mg used less rescue medication vs. placebo NNT to prevent an event 7.8, 95% CI: 6-11) in 6 studies (moderate quality evidence). The efficacy of acetaminophen 500mg–650mg did not prove superior to placebo. Further, acetaminophen 1000mg did not differ from either ketoprofen 25mg or ibuprofen 400mg (low quality evidence). Adverse events also did not differ between acetaminophen 1000mg and placebo (risk ratio [RR] 1.1, 95% CI: 0.94–1.3; high quality evidence). 

Study authors noted that for comparison studies of acetaminophen 500mg–650mg vs. placebo and acetaminophen 1000mg with active comparators, the evidence was downgraded to low or very low quality due to the small number of studies and events. 

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