Stimulant vs. Non-Stimulant Pre-Workout (Guide for First Timers)

Scooping some pre-workout shouldn't be synonymous with all-day jitters or an all-nighter. While some pre-workout powders may have you feeling like you've gulped down a thermos full of espresso, others offer a more mellow increase in energy levels.

Pre-workout formulas come in two forms: Stimulant (stim) and non-stimulant (non-stim).  The main difference between the two is that stimulant pre-workout supplements contain caffeine.  

Below, learn all about the differences between stim and stim-free pre-workout supplements and how they can affect your body and your workouts. 

Stimulant Pre-Workout Supplements

How They Work 

Stimulant pre-workouts contain caffeine. Considered the most widely used drug, caffeine is a stimulant in the way it increases the activity in your central nervous system and brain. According to the FDA, a stimulant is a drug that provides mental alertness or wakefulness when you're feeling tired or drowsy.

Adenosine is a neurotransmitter in the brain that brings on fatigue and tiredness, and caffeine works by blocking adenosine's effects. Caffeine latches onto adenosine receptors in your brain, blocking the adenosine from attaching to those receptors and causing fatigue. This mechanism, in turn, helps you feel more alert.

Stim pre-workouts contain anywhere from 100 to 300 milligrams of caffeine per serving, which is in line with the FDA's guidelines to consume less than 400 milligrams of caffeine in a day. Because stim pre-workout supplements contain caffeine, you're more likely to feel that big energy boost, but they can also come with other side effects like the jitters, especially if you're sensitive to caffeine.  

Benefits of Stim Pre-Workout Supplements

Most research on pre-workout supplements use pre-workouts that contain caffeine. According to a 2022 study in the International Journal Of Environmental Research And Public Health and a 2018 study in Critical Reviews In Food Science And Nutrition, taking stim pre-workout can offer the following benefits:

• Increased energy

• Improved strength

• Improved athletic performance 

• Enhanced mental focus

• Fat loss

Cons of Stim Pre-Workout Supplements 

If you wouldn't drink a cup of coffee past 2pm, you shouldn't take a stim pre-workout. Stimulant pre-workout supplements are not ideal if you usually work out in the evening or if you're sensitive to caffeine.

Let's dive a little deeper into the potential disadvantages of taking stimulant pre-workout supplements: 

• Caffeine sensitivity: Some folks are more sensitive to caffeine than others, and it actually boils down to our genetic makeup. Specifically, a variation of the ADORA2A gene determines our individual sensitivity to caffeine and its effect on sleep, per a 2012 report in Sleep. If you're sensitive to caffeine (in other words: you metabolize caffeine slowly), you'll probably experience jitters, restlessness, nausea, or anxiety after taking a stim pre-workout.

• Sleep disturbances: Caffeine keeps you awake, so you need to be wary of how late in the day you consume it so that it doesn't mess with your sleep. A 2023 study in Sleep Medicine Reviews looked at how coffee (containing 107 milligrams of caffeine) and a pre-workout supplement (containing 217 milligrams of caffeine) affected participants' sleep. Based on the findings, researchers suggest taking a caffeine-containing pre-workout supplement at least 13 hours prior to bedtime to avoid any sleep disturbances. 

Non-Stimulant Pre-Workout Supplements

How They Work 

Unlike stim pre-workouts, non-stimulant pre-workouts do not contain any caffeine. Instead, they often include a combination of amino acids, vitamins, minerals, and other nutrients or ingredients that help support athletic performance and muscle recovery and/or increase blood flow. 

For example, Transparent Lab's Stim-Free Pre-Workout Supplement contains the following research-backed active ingredients:

• Citrulline malate: L-citrulline is a non-essential amino acid, and when combined with malate, it's been shown to increase working capacity (or the number of reps you can complete in a set). That's because citrulline is considered a nitric oxide booster that helps increase blood flow, per a 2022 study in the Journal of Preventive Medicine and Hygiene. What's more, citrulline helps improve athletic performance, especially in high-intensity workouts with short rest times, as well as helps reduce muscle soreness, per a 2010 study in the Journal of Strength and Conditioning Research. 

• Beta-alanine: If you've ever noticed that tingly sensation after taking pre-workout, that's beta-alanine. This non-essential amino acid has been shown to delay muscle fatigue and increase aerobic power, muscular endurance, and efficiency, per a 2008 study in the Journal of the International Society of Sports Nutrition. 

• Betaine anhydrous: Betaine is a compound made by the body that can improve muscle endurance and the quality of reps performed, per a 2009 study in the Journal of the International Society of Sports Nutrition.

• Taurine: Taurine is a non-essential amino acid, meaning, our bodies can produce it naturally on their own. Research shows that when taurine is combined with branched-chain amino acids (BCAAs), which are essential amino acids, the combo can help reduce muscle soreness from high-intensity exercise, per a 2013 study in Advances in Experimental Medicine and Biology. 

Pros of Non-Stim Pre-Workout Supplements 

• No jitters or crashes: Because non-stim pre-workout supplements don't contain caffeine, you won't experience the jitteriness or crashes associated with the stimulant. But note that if your stimulant-free pre contains beta-alanine,  you'll probably feel a tingly sensation in your skin — while it's not so akin to jitters, it is noticeable.

• Better muscle endurance: Many ingredients in stim-free pre-workouts, such as citrulline and betaine anhydrous, are meant to support muscle endurance. Better muscle endurance means you can push through your workout and boost your exercise performance. The better you work out, the faster you'll notice muscle gains and get to your goals.

• Increased blood flow: Nitric oxide boosters such as l-citrulline can help open up the blood vessels and increase blood flow to the muscles. 

• They're ideal for people who work out in the evening or at night

• They're a great alternative for people who are sensitive to caffeine

Cons of Non-Stim Pre-Workout Supplements 

• They don't provide the same energy boost as stimulant pre-workouts containing caffeine

Choosing Between Stimulant and Non-Stimulant Pre-Workout Supplements

When it comes to stim vs. non-stim pre-workout supplements, you'll want to consider the time of day you work out, how sensitive you are to caffeine, and how much total caffeine you consume on a daily basis (including stim pre-workout supplements).

When to Choose Stim Pre-Workout Supplements

Because caffeine gives you that coveted spike in energy levels, stim pre-workouts are perfect if you:

• Work out in the morning

• Are often tired in the morning

• Want a noticeable energy boost

• Aren't super sensitive to caffeine and can handle taking the stimulant in the afternoon without it causing sleep disturbances

When to Choose Non-Stim Pre-Workout Supplements

Stimulant-free pre-workout supplements are less of a commitment: You can take them at any time of day without worrying about potential side effects from caffeine such as jitters or sleep disturbances.

Stimulant-free pre-workouts are great if you:

• Work out in the evening or at night

• Are sensitive to caffeine (i.e. you're a slow metabolizer)

• Are avoiding caffeine due to a medical condition (such as high blood pressure) or if you're pregnant or breastfeeding

• Take medications that interact with caffeine

• You drink a lot of caffeine-containing beverages such as coffee or tea throughout the day (you shouldn't consume more than 400 milligrams of caffeine in a day, per to the FDA)

Combining Stim and Non-Stim Pre-Workout Supplements

If you're having a hard time choosing between stim and non-stim, and feel like both pre-workout supplements can have a place in your fitness regimen, you can certainly stock up on both. 

Combining, or stacking, pre-workouts can offer the benefits of both.

Try taking half the serving size of each pre-workout — that means you'll get all the recovery-supporting ingredients in caffeine-free pre-workout supplements along with a smaller dosage of caffeine from the stim product, which means fewer and less severe caffeine-related side effects (like jitters and fast heart rate).

Safety Tips and Recommendations 

If you have a health condition or are on medication, always speak to your doctor before starting a new supplement. Pre-workouts, whether they're stim or non-stim, can contain ingredients that can interact with certain medications or affect the status of your health condition, so it's best to get the green light from your healthcare provider before buying a tub or two.

If you're going for a stim pre-workout, make sure not to take it too late in the day because caffeine can prevent you from falling asleep, and sleep is essential for healthy energy production, muscle growth, and recovery.

Last, but certainly not least, always choose third-party-tested pre-workout supplements. A dietary supplement that's third-party-tested is verified for purity and potency, so you can feel confident that your supplement is free of any potentially harmful ingredients.

The Bottom Line

Ultimately, choosing a stim vs. non-stim pre-workout boils down to when you'll use the supplement and whether or not you want that extra caffeine.

People who work out in the morning and folks who feel like they need caffeine to complete a workout would likely fare best with a stimulant pre-workout because it provides that apparent energy boost. On the contrary, after-work exercisers and people who are sensitive to caffeine should probably choose a stimulant-free supplement instead in order to avoid any caffeine-related side effects.

If your workout schedule is erratic — say, you work out after 5pm on weekdays and before 2pm on weekends — you might want to invest in both stim and non-stim pre-workouts. That way, you can use the stimulant-free pre-workout supplements on days that you hit the gym in the evening and then use the stim pre-workout on weekends when you work out earlier in the day.