Many people can’t live without their daily coffee, and coffee can actually be good for you. A 2015 study in the journal Circulation found that moderate coffee consumption (three to four cups daily) was associated with an 8 to 15 percent reduction in the overall risk of death.
- The Food and Drug Administration (FDA) says healthy adults can consume up to 400 milligrams a day of caffeine (about four or five cups of coffee) without dangerous, negative effects.
- But not everyone can drink even that much. Some people are naturally more susceptible to the effects of caffeine, certain medications may make people more sensitive to caffeine, and people who are pregnant, trying to become pregnant, or breastfeeding should not consume that amount. Talk to your doctor if you have any concerns about whether to limit caffeine intake.
- The FDA has not set a level of caffeine consumption that is considered safe for children, but the American Academy of Pediatrics discourages the consumption of caffeine and other stimulants by children and adolescents.
What Happens When You Have Too Much Caffeine?
When consumed in excess, the caffeine in coffee can be bad for you, causing side effects such as:
- Anxiousness
- Fast heart rate
- Feeling jittery
- Trouble sleeping (insomnia)
- Upset stomach
- Headache
- Nausea
- Feeling unhappy
Caffeine can also cause or worsen symptoms of anxiety or panic disorders.
In addition, it is recommended to drink coffee that is filtered with paper filters (paper filters work better than metal filters, such as those used to make French press coffee), because unfiltered coffee is associated with higher rates of early death. Unfiltered coffee may raise blood levels of a compound called homocysteine, which can raise levels of LDL (“bad”) cholesterol, increasing the risk of heart disease and stroke.
Many people also add lots of sugar or creamer to coffee, which can add fat and empty calories. Coffee, like anything else you consume, is fine in moderation.
If you experience any of the side effects listed above, you should try to cut back on your coffee consumption and see if your symptoms improve. If you are still having negative side effects, you should see your healthcare provider.
From 
https://www.health.harvard.edu/blog/the-latest-scoop-on-the-health-benefits-of-coffee-2017092512429
https://www.fda.gov/consumers/consumer-updates/spilling-beans-how-much-caffeine-too-much
https://pubmed.ncbi.nlm.nih.gov/10648261/