The effects of caffeine on one’s mental state are an important area for scientists to explore because about 90 percent of the world’s adults take the stimulating substance. Some prefer coffee, some tea, others soda pop and a few more take it in energy drinks. Caffeine is also in chocolate, over-the-counter pain relievers and even caffeine mints, including Viter Energy Mints.
But the health and wellness communities have long debated the pros and cons of caffeine, with the latter touching on its effects on mental health. Some studies show that caffeine can help alleviate symptoms of depression, while others say it worsens the condition.
Scientists debate whether caffeine has a positive or negative effect on people suffering from depression, a disorder affecting 15 percent of people in high-income nations. 
WHAT THE STUDIES SAY
Some scientists say caffeine helps alleviate symptoms, thanks to its positive effects that are so great it may actually help prevent suicide. There are numerous studies that have shown caffeine – specifically coffee - may prevent mild to moderate depression:
A group of Chinese scientists studied caffeine and its effects on the psyche and depression from 1980 to 2015.  Those researchers concluded caffeine caused depression in about 1 percent of people. But the Chinese studies also found that depression was less a risk among test subjects who increased their intake of caffeine each day. The upshot of these Chinese studies was that taking caffeine and coffee actually reduced the incidence of depression.
A group of researchers, from Europe, published a study of caffeine’s effects or risks with respect to depression. An analysis of 12 studies looked at the relationship between caffeine and depression, in 346,913 individuals and 8,146 cases of depression. Their conclusion? “This study suggests a protective effect of coffee on risk of depression.” 
This means that caffeine, particularly in coffee, may lessen the likelihood of depression.
By the way, this same study also found that tea, with its lower caffeine content per cup, was less protective in preventing against depression, but still effective to some extent.
Researchers from Qingdao University Medical College in China analyzed the results of 15 studies performed in the past on the potential link between coffee consumption and depression. The analysis found an 8 percent risk reduction in depression for each “cup/day increment in the coffee intake.” The study concludes that “coffee and caffeine consumption were significantly associated with decreased risk of depression.”
HOW CAFFEINE CAN HELP DEPRESSION
While there are no studies yet on how exactly coffee actually prevents depression, the researchers from Qingdao University Medical College put forward a couple of possible explanations.
Firstly, they speculated coffee may help prevent depression because it has chemical compounds that counteract depression.  Coffee combats depression through compounds that reduce inflammation in the nerve cells in depressed people’s brains. The compounds are caffeic acid, chlorogenic acid, and ferulic acid.
They suggested in the study:
“Along with caffeine’s natural antioxidant properties, coffee can act as an anti-inflammatory in affected parts of the brain. This may relieve some of the discomfort and distress caused by depression, which is related to inflammation.”
The other hypothesis is based on the psychostimulant nature of caffeine – it boosts motivation and helps you feel more awake.
Caffeine helps the brain create more dopamine, which activates the part that taps reward perception. This then allows you to make better decisions, feel more motivated, and generally be in a happy mood.
Based on a review conducted by A. Nehlig, having 75mg of caffeine (a cup of coffee) every 4 hours can lead to a “pattern of sustained improvement of mood over the day.” It can increase alertness and well-being, help concentration, improve mood and limit depression. 
Some research has found that copious amounts of coffee and caffeine can worsen one’s mental state. Coffee and/or caffeine taken in large amounts can result in headaches, anxiety, nausea, restlessness, increased blood pressure and palpitations.
Medical News Today says these symptoms are part of the fight or flight process. If the fight or flight symptoms occur too often from caffeine, inflammation and disease could result. 
Coffee consumption may result in a heightened risk of depression, some studies have shown. One study says taking caffeine might intensify depression and result in anxiety if the person has a mood disorder.
Further, caffeine’s effects are temporary, and depressed people could experience a crash in their mood when it wears off. “People who have depression are advised against consuming large amounts of caffeine,” Medical News Today concludes.
Mayo Clinic says that while there isn’t a clear link between caffeine consumption and depression, the idea may have been based on two things: 
Caffeine can cause sleep problems that affect mood. Caffeine can make it harder to fall asleep and stay asleep. Lack of sleep can worsen depression. If you have trouble sleeping, don’t drink caffeinated beverages late in the day. Some people need to limit caffeine to the morning or quit drinking caffeinated beverages completely to avoid sleep problems. Also, anxiety and depression often occur together, and caffeine can worsen anxiety.
Stopping abruptly can worsen depression. If you regularly drink caffeinated beverages, quitting can cause a depressed mood until your body adjusts. It can also cause other signs and symptoms, such as headaches, fatigue, and irritability.
Caffeine does more than just wake you up. It’s the most widely used stimulant/substance/drug (however way you want to call it) for getting that familiar jolt in the morning, the kick that you need to jumpstart the day.
Every day, millions of people all around the world consume caffeine to stay awake and ease fatigue. But there’s definitely more to it than just a fix.
While it usually gets a bad rap for its adverse effects like jitters and link to depression (usually from having too much of it too soon), moderate caffeine consumption can give you the best bang for the cup.
Erectile dysfunction. In combination, those are two of the ugliest words known to man. But can caffeine help you get it up?
Science hasn't found the definitive answer to this question, but one study concluded that fewer men who consume caffeine have problems performing. The study said:
Caffeine intake reduced the odds of prevalent ED, especially an intake equivalent to approximately 2-3 daily cups of coffee (170-375 mg/day). This reduction was also observed among overweight/obese and hypertensive, but not among diabetic men. Yet, these associations are warranted to be investigated in prospective studies