What does pre-workout do? The science behind the boost

Pre-workout supplements are everywhere. From gym floors to supermarket shelves, they're marketed as the secret to training harder, lifting heavier, and recovering faster. But with so many products, formulas, and bold claims, it's natural to ask: what does pre-workout do exactly?

The short answer: pre-workout supplements may support energy, focus, and exercise performance in some people. The longer answer? It's more complicated than the marketing suggests.

Not all pre-workouts are created equal. Different brands use different blends, and while some ingredients are backed by research, others are less convincing. So, are pre-workouts the missing link in your training routine, or just another wellness trend in a shiny tub?

Let's break down the science, the common ingredients, the benefits and risks, and what women should consider before adding pre-workout to their fitness routine.

What are pre-workouts?

At its simplest, a pre-workout supplement refers to a category of products designed to be taken before exercise.

The most common type comes in powder form, mixed with water to create a flavoured drink. But they're also available in ready-to-drink cans, concentrated shots, or even gummies.

In the UK, pre-workout supplements are sold as food supplements rather than medicines, meaning they are not regulated to the same standard as prescription treatments [1]. Quality, safety, and effectiveness can therefore vary between brands.

This is where confusion and sometimes hype set in.

What does pre-workout do?

The goal of pre-workout is straightforward: to give you a temporary boost before you train. Depending on the formula, pre-workout supplements may:

• Support alertness and focus, often via caffeine
• Reduce the perception of fatigue during high-intensity exercise
• Improve blood flow to muscles, helping with nutrient delivery
• Support endurances or power in short bursts

Research suggests some multi-ingredient pre-workouts can support exercise performance, particularly in endurance and strength [2]. But responses vary widely. Some people feel energised and focused, while others notice little difference or uncomfortable side effects.

And importantly, pre-workout won't replace the fundamentals of fitness. Consistent training, balanced nutrition, and adequate sleep remain the cornerstones of progress.

Types of pre-workout?

Not all pre-workouts look the same. Broadly, they fall into two categories:

Natural

You don't necessarily need a supplement to fuel your workout. Everyday foods and drinks can offer similar benefits:

• Coffee or tea can be a natural source of caffeine for energy and focus
• Bananas or other fruit are quick-digesting carbs to support energy production [3]
• Oats with nut butter give you longer-lasting carbs with some protein and healthy fats
• Beetroot juice is high in nitric oxide precursors, which may support blood vessels and circulation [4]

These options are affordable, accessible, and free from artificial additives often found in commercial pre-workouts.

Supplements

Commercial pre-workouts usually fall into:

• Stimulant-based: Built around caffeine and similar ingredients for alertness and increased energy
• Stim-free: Designed for those who avoid stimulants, often relying on amino acids, creatine, or nitric oxide boosters

Stim-free pre-workouts may be preferable for women who train in the evenings or who are sensitive to caffeine.

What is typically in them?

Most pre-workout supplements share a similar set of ingredients. Here are some of the most common pre-workout ingredients you'll see on labels:

• Caffeine supports alertness and may delay perceived fatigue [5]. Too much can cause jitters, anxiety, or sleep disruption [6].
• Beta-alanine helps buffer lactic acid, potentially delaying fatigue during intense exercise [7]. It can cause harmless tingling in the skin [8].
• Creatine is one of the most researched supplements for short-burst power and muscle strength [9]. Typically effective at ~3-5g per day.
• Citrulline or arginine are amino acids that support nitric oxide production, which may aid blood flow [10].
• BCAAs (branched-chain amino acids) are sometimes included for muscle support, though whole protein sources are generally more effective [11].
• Tyrosine is occasionally added for focus and mental performance [12].
• Electrolytes and vitamins are sometimes included for hydration and energy metabolism.
• Artificial sweeteners are added for flavour, though some people prefer to avoid them.

Formulas vary widely. Some contain research-backed doses, while others underdose key ingredients or over-rely on stimulants.

What pre-workout ingredients should you avoid?

Not all ingredients are safe or necessary. Watch out for:

• Excessive caffeine: High doses (over 300mg) can cause jitteriness, elevated heart rate, and poor sleep [13]
• Unlisted stimulants: Some imported products have been found to include unapproved compounds.
• Proprietary blends: Vague labels that don't disclose how much of each ingredient you're consuming.
• Artificial additives: Not unsafe for most, but some prefer to avoid artificial colours, flavours, or sweeteners.

If you're considering a supplement, look for third-party tested products with transparent labelling. However, those with high blood pressure or other health conditions should still be cautious about taking pre-workout. It's always best to discuss any changes to your supplement routine with a health professional first.

What are the benefits of pre-workout?

When used appropriately, pre-workout may offer several potential benefits.

Many women find they feel more energised and motivated, which can be especially helpful for early-morning workouts or sessions squeezed in after a long day.

Certain formulations have been studied for their role in improving endurance and strength, which may make it easier to push through challenging sets or sustain longer training sessions.

Pre-workout may also reduce the perception of fatigue, meaning tough workouts feel more manageable.

For some, the ritual of mixing and drinking a pre-workout becomes part of the routine itself, providing a psychological boost that helps maintain consistency over time.

It's important to keep in mind, however, that the benefits aren't universal. Individual responses may vary, and not every product will live up to the promises on its label.

Is it really necessary to take pre-workout?

In short: no.

Pre-workouts are optional, not essential. Many people reach their fitness goals through consistent training, good nutrition, hydration, and rest, without ever touching a supplement.

If you often feel low-energy before workouts, a balanced snack or a strong coffee may work just as well. Pre-workout can be seen as a convenient "extra", not a requirement.

Who should not take a pre-workout supplement?

Pre-workouts aren't suitable for everyone. You may want to avoid them if:

• Are pregnant or breastfeeding
• Have high blood pressure, heart conditions, or anxiety disorders
• Are sensitive to caffeine or stimulants
• Are taking medications that interact with stimulants
• Are under 18

If in doubt, speak with your doctor before starting any supplement.

Does pre-workout help in building muscle?

Pre-workout supplements don't directly build muscle. Muscle growth comes from progressive resistance training, adequate protein intake, and recovery.

That said, pre-workout may indirectly support muscle development by helping you train harder or longer. Over time, this can contribute to improvements in strength and performance, but only when combined with the fundamentals.

Can you use pre-workout with weight loss injections?

With weight loss injections such as Wegovy and Mounjaro now available in the UK, many women wonder if these treatments can be combined with pre-workout supplements.

Since both pre-workout supplements and GLP-1 medications affect energy, appetite, and exercise tolerance, it’s important to understand how they might overlap.

Currently, there is no evidence of a direct interaction between weight loss injections and the common ingredients in pre-workout products, such as caffeine, creatine, beta-alanine, and amino acids. For most healthy adults, these supplements are generally considered safe when used as directed.

That said, there are a few things to keep in mind:

• Caffeine sensitivity: Some women on GLP-1 treatments report feeling more sensitive to stimulants, which may increase the chance of jitters, nausea, or disrupted sleep when taking pre-workout.
• Digestive effects: Because GLP-1 injections slow digestion, adding high-stimulant pre-workout supplements may sometimes make digestive discomfort worse.
• Hydration and nutrition: Both weight loss injections and pre-workout can influence appetite, hydration, and electrolyte balance. Supporting your body with adequate fluids and balanced nutrition remains essential.

If you’re using weight loss injections and thinking about taking pre-workout, it’s always best to speak with your GP or Juniper practitioner before adding supplements to your routine.

Sustainable energy with Juniper

At Juniper, we know lasting results don't come from powders or quick fixes — they come from building sustainable habits, supported by evidence-based care.

The Juniper Programme combines weight loss medication with dietitian-led health coaching and tracking, so you can lose weight and reach your goals for good.

Kickstart your weight loss journey with Wegovy or Mounjaro, two groundbreaking weight loss medications that mimic the GLP-1 and GIP hormones, respectively, to help control cravings, delay stomach emptying, and keep you feeling fuller for longer. These clinically backed treatments help members experience up to 20% body weight loss.

Plus, we have a team of expert dietitians and health coaches you can consult with to help you work through any challenges you're experiencing during your weight management journey. This approach sets you up for sustained weight loss, rather than a quick-fix solution.

This means you can continue to enjoy the things you love in moderation without ever feeling deprived.

Ready to see if Juniper is right for you? You can check your eligibility here.

Frequently asked questions

Pre-workout supplements raise a lot of curiosity, especially around their effects on women’s health, exercise performance, and long-term safety. Beyond the basics of what they do, it's also important to know about side effects, best timing, and how often you can take these products.

What is the best type of pre-workout for women?

The best type of pre-workout depends on your goals and tolerance. Many pre-workout supplements for women focus on lower caffeine content, balanced amino acids, and ingredients that support endurance and muscle recovery without overstimulation. Stim-free pre-workout formulas may be a good option for those training later in the day or with sensitivity to caffeine.

Can pre-workout supplements support weight loss?

Pre-workout supplements are not designed for weight loss directly, but by helping you increase energy and push through workouts, they may support higher calorie burn and improvements in body composition. Sustainable weight loss still depends on nutrition, resistance exercise, and overall lifestyle habits.

Can pre-workout mess with hormones?

There’s no strong evidence that pre-workout supplements directly affect hormone levels in healthy adults. However, high caffeine intake from many pre-workout formulas can influence stress hormones like cortisol and may impact sleep, which in turn can affect overall hormonal balance.

Does pre-workout affect skin?

Some people notice tingling or flushing after taking pre-workout, usually due to beta-alanine or niacin. These effects are harmless but can feel uncomfortable. In rare cases, artificial sweeteners or other stimulants may trigger breakouts or irritation in sensitive individuals. Choosing third-party tested pre-workout products with transparent ingredient lists can help minimise unwanted skin reactions.

How many times a week can you take pre-workout?

Most pre-workout supplements are safe for healthy adults to use a few times per week, especially around high-intensity exercise or strength training sessions. Taking a pre-workout every day is not necessary and may increase the risk of building caffeine tolerance, poor sleep, or other adverse effects. Cycling your use or saving it for your hardest workouts can help maintain effectiveness.

When is the best time to take pre-workout?

The best time to take pre-workout is generally 20–30 minutes before your workout, allowing the ingredients to be absorbed and support energy production. If you train late in the day, consider stim-free formulas to avoid sleep disruption. Women with sensitivity to stimulants may find morning or midday workouts are the best time for taking pre-workout supplements.

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