Curcumin has been shown to be safe in numerous human studies, with only minor toxicity associated with the molecule. This is in part why it is increasingly being viewed as a biomolecule capable of being administered for an extended period without causing side effects. 

Side effects of headaches, nausea, vomiting and/or diarrhoea, stomach pain and constipation happen in more than 1 in 100 people taking omeprazole. More serious side effects after taking omeprazole for more than a year include bone fractures, gut infections and vitamin B12 deficiency as well as an increased risk of developing stomach cancer (1). 

Curcumin was shown to be effective in all of the subtypes of functional dyspepsia, and while both curcumin and omeprazole were both effective for functional dyspepsia they did not seem to have a synergistic effect. Interestingly patients with a high body mass index indicated a trend towards liver function impairment in the curcumin group, and so larger studies are needed. However, this could indicate a common issue with the reductionist method of extracting isolated compounds from plants instead of administering whole plant extracts in their more natural and traditional preparations. Normally herbalists administer whole turmeric preparations to support liver function. Isolating a compound from the plant means we lose the synergy effect which can both decrease safety and efficacy.

Curcumin is an isolated compound found in turmeric and is administered here in high concentrations. Although curcumin is naturally found in turmeric, it is not normally present in such high levels. However, the chemical complexity of more traditional natural extracts means that there is a whole array of other medicinal compounds found that can contribute synergistically to both the therapeutic efficacy of the plant and its safety.