Why is Caffeine in Pre-Workout Supplements?

A guide to the most common PWO ingredient

A guide to caffeine in pre workouts

Disclaimer: This post has not been written or reviewed by a medical professional. Under no circumstances should it be used as medical advice to diagnose, prevent or treat any illness, disease or medical condition. You use the information at your own risk.

If you’ve recently started researching pre-workout supplements, it won’t take long before you realise that most include caffeine.

In fact, caffeine is such an important ingredient that you should assume every pre workout that isn’t labelled as stim-free, caffeine-free or similar contains it.

This isn’t a bad thing – seriously!

Although caffeine has had some negative press – and some of it is justified – it has a number of proven benefits, including increased focus, alertness, pain tolerance and fat burning.

It’s important to understand why an ingredient is effective though. As I mention here, you shouldn’t just take the pre-workout brand’s word for it. Here’s a quick look at what caffeine is, what it does and why you should consider taking it.

TIP: Want to learn more about pre-workout supps? Check out our full guide here.

What Exactly is Caffeine?

Caffeine is a type of central nervous system stimulant that’s naturally found in coffee beans. It can also be artificially created in a lab. No matter where the caffeine originally comes from, it has the same molecular structure.

This isn’t a biology lecture, so I won’t go into too much detail about how caffeine works at a molecular level.

All you really need to know is that it prevents adenosine from acting upon adenosine receptors. As adenosine causes relaxation and sleepiness, caffeine has the effect of making us feel more alert. Caffeine also has a stimulatory effect on parts of the nervous system (more on that in a moment).

It’s also worth pointing out that the effects of caffeine vary depending on how often it is taken and a person’s genetics.  This means you may experience the effects of caffeine differently to others.

What Are The Advantages of Taking It Before a Workout?

While the merits of our coffee-addicted culture are open to debate, there’s no doubt it’s one of the best ingredients for getting a quick energy boost.

How effective is it really when it comes to boosting athletic performance though?

Caffeine has a number of positive effects when taken before a workout. It’s not going to turn you into a superhuman, but it can have a noticeable effect. Some of the benefits include:

  • Improved strength [1] – There is evidence that caffeine can increase strength, but only in individuals without an existing tolerance.
  • Enhanced anaerobic performance [2] – This may be due to a combination of increased power output and fatigue-fighting properties.
  • Sped up metabolism [3]Caffeine seems to increase metabolic rate in some people.
  • Increased training volume [4] – Some people are able to complete a larger amount of work after taking caffeine than without.

There are a number of other potential benefits to taking caffeine. These include relief from muscular pain and post-gym soreness, replenished glycogen stores and an enhanced feeling of alertness.

In short, many people can benefit from taking caffeine before a workout. Even so, it’s vital to track your total caffeine consumption – including from coffee, tea, pre workouts and other beverages – so you can avoid taking too much or building a tolerance.

A man doing bench press

A Quick Overview of Doses

As you know, caffeine is found in a variety of drinks, including tea, coffee, cocoa and guarana. It’s also an ingredient in many energy drinks and sodas, and can be bought in pill form.

ow you take caffeine (pill or drink) doesn’t seem to alter its effects. Some people prefer to gain additional benefits by taking it from natural sources (such as green tea), although this can make it harder to take a precise dose.

To give you some context, here’s a quick overview of the caffeine content of common beverages:

  • Bang Energy Drink (16 oz.) – 357mg
  • Panera Light Roast Coffee (regular 16 oz.) – 300mg
  • Starbucks Espresso (doppio, 2 oz.) – 150mg
  • Diet Coke (20oz.) – 76mg
  • Nespresso capsule – except Kazaar (2 Tbs, makes 12 oz.) – 50-80mg
  • Maxwell House Lite Ground Coffee (2 Tbs, makes 12 oz.) – 50-100mg
  • Red Bull (8 oz.) – 80mg
  • Coca-Cola, Coke Zero (20 oz.) – 57mg
  • Black tea, brewed (8 oz.) – 47mg
  • Green tea, brewed (8 oz.) – 29mg
  • Decaf ground coffee (2 Tbs, makes 12 oz.) – 2-10mg
  • Decaffeinated tea, black, brewed (8 oz.) – 5mg
  • Herbal tea, brewed (8 oz.) – 0mg

What is the Optimal Dose for Training?

Most pre-workout supplements contain around 150mg – 300mg. This puts them somewhere between an espresso and a high-caffeine energy drink.

What’s the optimum dose before a workout though?

If you don’t have a tolerance for caffeine, a  dose of as little as 0.3mg/kg of bodyweight can be noticeable. For this reason, the “best” dose varies greatly depending on the individual.

There probably isn’t much benefit to going over 3mg/kg of bodyweight though. Not only do the positive affects seem to plateau, but you’re more likely to suffer from increased anxiety and stress.

As I mentioned earlier, how you take caffeine doesn’t change its effects. If you have an espresso when you wake up, two diet cokes in the morning then a pre-workout supplement with 150mg after lunch, you’ve taken a lot of caffeine in a short space of time.

For this reason, it’s often a good idea to drink decaffeinated coffee and other drinks if you’re taking a pre-workout.


The effects of caffeine can be relatively quick. It can take over an hour to reach peak bloodstream levels though, so it’s a good idea to take caffeine around 60-minutes before your workout.

There’s an important factor to consider though: your sleep quality.

If you workout in the evening, the six-hour half-life of caffeine means you could be kept awake.


As anyone with a coffee addiction knows, regular caffeine can build up tolerance. This can happen relatively quickly – especially at high doses.

What’s interesting is that not all benefits of caffeine are affected by an increased tolerance. If you are taking caffeine purely for endurance, for example, then you probably don’t need to cycle.

If, however, you want enhanced alertness, mood, fat burning and focus, then cycling is a good idea.

The length of time required to cycle caffeine depends on the individual. Not taking any caffeine for 3-4 weeks usually reduces tolerance, but it may take up to two months.

What Dose of Caffeine is Dangerous?

This varies a lot depending on the individual, so it’s hard to give a one-size-fits-all answer.

For the average healthy adult, anything up to 400 mg/day is probably safe. The limit is much less for pregnant and breastfeeding women though (around 200mg according to the EFSA). People with a cardiovascular problem should also minimise the amount of caffeine they drink.

While you may be able to drink more than 400mg in a day without serious side effects, higher doses increase the chances of negative side effects. It can also reduce the positive effects (see the cycling section above to prevent this).

Caffeine can even be deadly in high enough doses. Examine.com states that 15 mg/kg of body weight is toxic and 150mg/kg is potentially lethal.

In practice, this would require drinking a huge amount of caffeine in a short period of time. It’s much more likely with powdered caffeine though, so be very careful and double check your measurements.

What Are The Downsides or Side Effects?

Like most things in life, there are both good and bad sides to taking caffeine before a workout. Anxiety or jitters, for example, are negative effects most coffee drinkers have experienced at some point.

The side effects vary depending on the individual, but here are some of the most common.

Insomnia or Interrupted Sleep

Everyone metabolises caffeine differently. Some people can sleep relatively soon after taking it without any issues. Others are much more sensitive.

For this reason, make sure you take note of how caffeine is affecting your sleep and anxiety. Some people don’t sleep properly for months or even years before they realise it’s caffeine causing the problem.


Caffeine is a mild diuretic. The effects are relatively minor – especially as caffeine is usually consumed as part of a liquid beverage – so it’s often not noticeable.

Even so, make sure you drink plenty of water when taking caffeine.

Increase Blood Pressure

Caffeine can increase short term blood pressure. People who are prone to higher blood pressures are affected more strongly in this regard.

The long-term blood pressure effects of taking caffeine aren’t as well established. Some studies appear to show an increase in blood pressure, while others don’t. Examine.com provides a layman’s overview of the competing evidence, so I recommend reading that article if you want to learn more.

Acid Reflux

A study seems to show that people who drink a lot of coffee could potentially suffer from acid reflux. This is because the caffeine and fluid combine to lower pressure of the “valve” located at the entrance to the stomach.


Caffeine is a mildly addictive drug. If you consume more than 200mg per day over an extended period (sometimes even less), you may experience withdrawal symptoms such as anxiety, depression and headaches. These can last over a week in extreme cases.

If you notice these symptoms, it may be a good idea to gradually reduce your caffeine usage rather than stopping cold turkey.


Caffeine is one of the most effective pre-workout supplements – so it’s not surprising to find it in most PWOs. It has a range of potential athletic benefits, including increased power output and anaerobic endurance.

It’s important to understand the side effects too though – especially as they can vary depending on the individual. If you think the downsides outweigh the benefits, there are plenty of non-stim pre-workouts on the market that don’t contain caffeine.


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