Evidence review: safety
The summary of product characteristics (SPC) for the omega-3 fatty acid medicines, Omacor and Teromeg, describe the only contraindication as hypersensitivity to the active substance, to soya or any of the capsule excipients. Moderate increases in bleeding time have been reported with high doses, therefore a special warning for use is described to make allowance for the increased bleeding time in people who are at high risk of haemorrhage and those taking anticoagulants.
The SPC for Maxepa also advises to use with caution in people with non-insulin-dependent diabetes with aspirin-sensitive asthma. This is alongside precautions to monitor people with bleeding disorders and drugs affecting coagulation.
Commonly reported side effects in the SPCs (occurring at a frequency between 1 in 10 and 1 in 100 people) include dyspepsia and nausea. Uncommon side effects (frequency between 1 in 100 and 1 in 1000 people) include gastroenteritis, hypersensitivity, dizziness, dysgeusia (distortion of taste), abdominal pain, gastrointestinal disorders, gastritis, and upper abdominal pain.
In the Cochrane review, most of the adverse event information came from the small, short-term study by Peet and Horrobin (2002) (n=122, 12-week follow-up). This reported that adverse events were rare and were not significantly different between omega-3 fatty acids and placebo. Further information from Fenton et al. (2001) (n=90, 16-week follow-up) found omega-3 fatty acids did not result in any drug-related movement disorders, but may be associated with diarrhoea.
The Cochrane review concluded that there were no differences between omega-3 fatty acids and placebo in the numbers of people leaving the studies early (n=595, 6 randomised controlled trials [RCTs], risk ratio [RR] 0.86; 95% confidence interval [CI] 0.50 to 1.48), suggesting that omega-3 fatty acids are tolerated as well as placebo in the short term.
The safety of omega-3 fatty acids was also reported in Emsley et al. (2008). This study reported safety outcomes for 72 people with schizophrenia who were included in the 12-week, double-blind RCT by Emsley et al. (2006), 47 of whom also entered a 40-week, open-label extension phase. Adverse event reporting was similar for omega-3 fatty acid (ethyl-eicosapentaenoic acid [E-EPA] 2 g/day) and placebo groups. During the 12-week blinded phase, there was a small increase in mean body mass index (BMI) and bleeding time in the omega-3 fatty acid group, but these were not statistically significantly different to the placebo group. There was a small absolute increase in mean BMI during the open-label phase of the study in people continuing to use omega-3 fatty acids, and decreases in total cholesterol and HDL-cholesterol levels.