Side effects of caffeine vary depending on how much caffeine you have consumed. It has both positive and negative effects. The type of effects depends on the amount of caffeine you consume and when you consume it:

  • Positive effects come from sticking to the recommended amount of caffeine intake every day, which is 400 mg.
  • One gram of caffeine taken in a single dose, which is equal to 6 strong cups of coffee will cause insomnia, restlessness, ringing in the ears, confusion, tremors, irregular heartbeat, fever, photophobia, vomiting, and diarrhea.
  • Severe intoxication caused by very high consumption can cause nausea, gastrointestinal hemorrhage, and convulsions,
  • The lethal dose of caffeine for a 200-pound adult is estimated to be 10 to 15 grams ingested within two hours. Lethal blood levels are typically above 80 to 100 mg/L.

Sudden withdrawal of caffeine after prolonged high consumption of caffeinated beverages can lead to withdrawal symptoms such as headaches, irritability, and difficulty in concentration.

Different people react differently to caffeine intake. Some are more sensitive to the effects of caffeine than others are.

Positive effects of caffeine

Positive effects accrue with the caffeine intake being within the prescribed limit of 400 mg per day. Due to its rapid absorption in the body, these short-term positive effects come into effect within 5 to 30 minutes after consumption. Caffeine

  • Lowers the risk of suicides. According to a new study, people who drank more than four cups of coffee a day were less likely to commit suicide than those who drank less than one cup a day. Caffeine blocks mood-depressing chemicals and stimulates the release of dopamine, which makes you feel happy.
  • Lowers rate of cirrhosis. Your body makes a chemical called paraxanthine from digesting caffeine. This chemical slows the growth of scarring of liver tissue involved in fibrosis. This may help fight liver cancer, alcohol-related cirrhosis, non-alcohol-related fatty liver disease, and hepatitis C.
  • Improves athletic performance. Caffeine fosters better use of glycogen, blood sugars, and body fat. Muscle glycogen serves as the main fuel for your muscles. Caffeine stimulates the use of fat as an energy source, thereby sparing glycogen and improving endurance leading to better performance in athletes.
  • Improves work efficiency. Extensive research has shown that caffeine consumption within the prescribed limits increases your alertness, concentration, and performance. It helps you stay focused, and concentrate better leading to improved work performance.
  • Can relieve a headache, even migraine. Any headache is caused by the widening of the blood vessels in the brain (vasodilatation). Caffeine has vasoconstrictive properties, meaning it narrows the blood vessels to restrict blood flow, thereby relieving the pain. Additionally, when caffeine is taken in combination with painkillers, such as aspirin, ibuprofen, or acetaminophen, it increases the absorption of the medication potentiating its action to provide faster relief.
  • Gives relief from asthma. Caffeine, as in a strong cup of coffee is known to improve airways function moderately in people with asthma. Its action lasts for up to four hours. It does this by relaxing the airways and reducing inflammation in the lungs, akin to the action of asthma medication theophylline. It also reduces the frequency of asthma attacks.

Harmful effects of caffeine in men and women

The negative effects of caffeine may be short-term or long-term and start accruing when you regularly cross the consumption safety limit of 400 mg from all sources per day.

Negative effects include:

1.  Premenstrual syndrome (PMS)

Many pre-menopausal women suffer from premenstrual syndrome (PMS), about a week or two before their period. Symptoms include bloating, headaches, difficulty in concentration, mood swings, and breast tenderness.

The American Congress of Obstetrics and Gynecology, and the Association of Reproductive Health Professionals, along with some other groups recommend that women who suffer from PMS should completely avoid caffeine.

2. Caffeine consumption may raise blood pressure. 

Caffeine in coffee or tea may temporarily cause a small rise in blood pressure but does not appear to have a long harmful effect. It does this because of its vasoconstrictor effect.

Thirty minutes after drinking a strong cup of coffee, your systolic and diastolic pressure may rise. The systolic may rise by about 15 points and this effect is short-term and lasts for about four hours.

This is not a long-term effect and it should not deter you from having your morning cup of tea or coffee, which could, in fact, be healthy for you.

3. Increased risk of heart attacks among young adults

Young hypertensive adults are at an increased risk of a heart attack if they regularly consumed more than 400 mg of caffeine daily. This means more than 4 cups of coffee.

However, the association between coffee drinking and the risk of coronary heart disease remains divisive as there are no concrete results from studies to confirm the same.

4. Is Caffeine linked to gout attacks?

Studies have found that drinking at least one cup of coffee daily reduced the risk of developing gout. It is possible that coffee consumption might lower a person’s risk of gout, but further studies are needed to support this.

5. Caffeine could cause incontinence.

A study from the University of Alabama showed that women who regularly consume excessive caffeine have a 70% increased risk of developing urinary incontinence.

6. Caffeine may cause muscle tremors

Too much caffeine stimulates your nervous system and can lead to muscle twitching, cramps, and spasms. Caffeine can cause small involuntary contractions of muscle fibers across the body. These muscle spasms could present in the form of a twitching eyelid or trembling hands.

7. Caffeine can cause stomach pain and GERD

Caffeinated food and beverages can increase gastric secretions leading to more acidity in the stomach. This can give rise to stomach pain. Caffeine may also relax the lower esophageal sphincter, causing the acid to reflux and cause heartburn.

People who consume regularly consumed caffeinated beverages in excessive amounts often report abdominal pain and heartburn. This mainly occurs when you consume caffeinated beverages on an empty stomach. This happens because caffeine stimulates the excessive secretion of acid in the stomach,

If you experience heartburn or stomach pain, it is best to minimize the amount of caffeine intake.

8. Caffeine can cause chronic headaches

While an occasional cup of caffeinated coffee can relieve a headache, overuse can be a modest risk factor for chronic daily headaches.

9. Caffeine could reduce fertility in women

According to Nevada Today, women who regularly consumed caffeine beyond the safety limit reduced their chances of becoming pregnant by 27%. Caffeine reduces the muscular contractility of the fallopian tubes due to which the forward movement of the ovum is disturbed.

This can reduce the chances of conception in women .who consume too much caffeine

10. Caffeine and miscarriage risk

There is a slightly increased risk of miscarriage in women who consumed too many caffeinated beverages during preconception days.

According to a new study from the National Institutes of Health and Ohio State University, Columbus, a woman’s chances of miscarriage are more if she drank more than two caffeinated beverages a day during the weeks before conception.

 11. Caffeine’s effect on type 2 diabetes

A study conducted by the American Diabetes Association revealed that caffeine impaired glucose tolerance in people with maturity-onset diabetes and acutely decreased insulin sensitivity in young, nondiabetic adults.

12. Worsens menopause symptoms

According to Medscape, caffeine intake is associated with more hot flashes and night sweats in menopausal women. However, there was no link with other menopausal symptoms such as problems with mood, memory, and concentration.

13. Effect on mental health

Caffeine is known for causing nervousness and anxiety, especially in higher doses. People who are already having underlying mental issues may be more susceptible to this effect of caffeine. Studies have shown caffeine aggravated symptoms of anxiety and depression.

14. Promotes weight loss

Caffeine itself contains very few calories, so it cannot you gain weight on its own. According to NIH, caffeine intake might promote weight loss, and reduce BMI and body fat. To receive these weight loss benefits, it is recommended to drink no more than four 8-oz cups of coffee a day, which equates to 400mg of caffeine.

15. Protects skin

Due to its powerful antioxidant properties, caffeine protects the skin cells against UV radiation. It also slows down the process of photoaging of the skin, which is skin damage caused by exposure to sunlight and ultraviolet (UV) light. Photoaging, the appearance of wrinkles and pigmentation on the skin occurs due to DNA changes at a cellular level.

Caffeine also finds use in cosmetics because it increases the microcirculation of blood in the skin. This helps reduce inflammation and puffiness. Due to its vasoconstrictor effect, it reduces blood flow to the skin and makes it appear brighter and smoother.

Caffeine intake leads to an increased stress response in the body. Stress hormones, such as cortisol, increase the amount of sebaceous secretions from your sebaceous glands. Sebaceous secretions are oily in consistency and excessive secretion can make you more prone to acne breakouts.

16. Weakens bones

Studies offer a mixed picture of the effect of drinking caffeine on your bones. Heavy caffeine consumption is reported to reduce bone mineral density (BMD) and negatively influence calcium retention. This results in an increased risk of osteoporosis and bone fractures.

17. Disturbs sleep

Once consumed, caffeine is very rapidly absorbed into the bloodstream through which it travels throughout the body including the brain. It’s here in the brain that it exerts its most powerful effect of making you more alert and keeping you wide awake.  Caffeine does this by blocking the adenosine receptors that are responsible for promoting sleep.

The half-life of caffeine is 4 to 6 hours, meaning that even after 6 hours, half of the caffeine is present in the blood after you have consumed it. Therefore, If you drink a caffeine beverage 6 hours before bedtime, it will keep you awake, not let you sleep, and will disturb your sleep pattern.

18. Increases intraocular pressure

Caffeine increases intraocular pressure when taken with or after exercise. For most people, this may not present much of a problem.

However, those suffering from eye disorders like glaucoma should be cautious when consuming caffeine beverages before, during, and immediately after physical activity.

19. Caffeine dependence

Caffeine has the ability to enhance concentration, increase metabolism, and boost mood. That is why we yearn for a cup of tea or coffee in the morning to elevate our mood.

People can develop a dependence on caffeinated beverages quite easily. When you drink caffeinated beverages on a regular basis, you begin to develop tolerance to it. You then start requiring more of it to make you alert and elated. You start to become dependent on caffeine to get that “caffeine fix”.

Your dependence on caffeine reaches such a point where you are unable to do your daily activities without caffeine. Stopping caffeine from such prolonged use can make you to have withdrawal symptoms like any other addicting drug such as nicotine and alcohol.

Signs of caffeine toxicity

  • Side effects such as restlessness, irritability, nervousness, vomiting, rapid heart rate, and tremors occur with a dose of 1 gram.
  • Caffeine toxicity has been seen with an intake of a single dose of 1.2 grams or more.
  • 10-14 grams of caffeine consumption at one time is fatal.
  • Caffeine intake of up to 10 grams has caused convulsions and vomiting, but the person can recover in about 6 hours.

Toxicity due to dangerous levels of caffeine in the blood is seen with the overuse of caffeine pills or tablets. It is not seen due to caffeinated beverages because a very large amount would be needed to be consumed within a few hours to reach toxic blood levels. For example, 10 gm of caffeine is equal to about 100 cups of brewed coffee.