Lemon coffee is also believed to provide relief from headaches and also boost digestion, however, there are a lot of contradicting studies on this issue. Some studies suggest that caffeine does have a vasoconstrictor effect (it tightens your blood vessels) which provides relief from headache, while others argue that excess caffeine intake can be a reason for headache.
Even in the case of diarrhoea, there is no clear study that can highlight how the drink can boost digestive health. When suffering from diarrhoea it is recommended to have solid foods to bulk up the stool. Drinking lemon coffee is not a good idea.
Due to a lack of evidence, claimed benefits of drinking lemon coffee cannot be verified. More research is needed in this area.