Can I drink coffee with citrulline? Understanding the Combination

October 21, 2025 •

5 min read

According to research published in Nutrients, taking caffeine can be ergogenic for muscular strength and endurance. Many individuals combine this with citrulline, an amino acid, to optimize workout performance, which begs the question: Can I drink coffee with citrulline?

Quick Summary

It is generally considered safe to combine coffee and citrulline for exercise, though studies suggest it may not provide significant additional benefits beyond caffeine alone for certain performance metrics. Some individuals report mild side effects like nausea or headaches when taken together, particularly at higher doses, while others tolerate the mix well. Timing the supplements 30-60 minutes pre-workout is common.

Key Points

Safety Profile: Combining coffee (caffeine) and citrulline is generally considered safe, with no major drug interactions reported.
Performance Impact: Some studies suggest that while caffeine significantly boosts muscular endurance and strength, adding citrulline does not necessarily provide additional ergogenic benefits beyond caffeine alone.
Mechanism of Action: Caffeine acts as a central nervous system stimulant, while citrulline promotes vasodilation by increasing nitric oxide, which improves blood flow.
Potential Side Effects: Co-ingestion may increase the risk of mild adverse effects such as nausea, headache, or dizziness compared to taking either supplement in isolation, especially at higher doses.
Optimal Timing: For pre-workout purposes, consuming the combination about 30-60 minutes before exercise allows the active ingredients to peak during your training session.
Dosage Matters: It is recommended to start with a moderate dose of both substances to assess tolerance before increasing, and always follow manufacturer guidelines for supplements.

For many, a successful workout relies on the right combination of energy and muscle support. Coffee, a staple for its stimulating caffeine, and citrulline, an amino acid lauded for enhancing blood flow, are popular choices. When considering combining them, it's important to understand how each works independently and what the potential combined effects might be. This article explores the science behind mixing coffee with citrulline, examining safety, performance, and practical advice.

The Role of Citrulline and Caffeine

To understand the combination, one must first grasp the individual roles of each compound in the body. Citrulline is an amino acid that converts into L-arginine and then into nitric oxide (NO) in the kidneys. This process is known as the nitric oxide pathway. The resulting increase in NO causes vasodilation, which is the widening of blood vessels. This leads to improved blood flow, delivering more oxygen and nutrients to working muscles. The potential benefits of this mechanism include:

Enhanced exercise performance and endurance.
Reduced muscle soreness and faster recovery.
Improved 'muscle pumps' during resistance training.
Positive effects on cardiovascular health, including blood pressure regulation.

Caffeine, on the other hand, is a central nervous system stimulant. It works by blocking adenosine receptors in the brain, a neurotransmitter that promotes relaxation and drowsiness. This action leads to a cascade of effects, including increased alertness, focus, and energy. While caffeine is a stimulant, its impact on blood vessels can be complex. For example, it can cause vasoconstriction (narrowing of blood vessels) in the brain, which is why it's used in some headache medications. However, its overall effect on exercise performance is largely due to increased alertness and reduced perception of effort, allowing athletes to push harder.

Combining Coffee and Citrulline for Performance

Given their distinct mechanisms—citrulline's focus on vasodilation and blood flow, and caffeine's role in mental and nervous system stimulation—it is logical to question whether combining them offers a synergistic effect. Many pre-workout supplements include both ingredients, and anecdotal reports suggest a powerful boost when taken together. The idea is that the stimulant properties of caffeine will kick in alongside citrulline's blood flow enhancement. However, scientific evidence on the additive benefits is mixed.

A randomized crossover trial from 2023, for instance, found that while caffeine improved measures of muscular strength and endurance, combining it with citrulline malate did not provide any additional benefit for those outcomes. In that study, caffeine alone was shown to be ergogenic, but adding citrulline didn't seem to enhance those specific effects further. This suggests that the primary performance-boosting effect in a coffee-citrulline combination might come mainly from the caffeine, at least for some individuals and exercise types. The theoretical benefit of enhanced blood flow from citrulline may not translate to a measurable additive performance gain in all scenarios.

Safety and Potential Side Effects

From a safety perspective, no major drug interactions have been identified between caffeine and citrulline. Both are generally well-tolerated by healthy individuals when taken in recommended doses. However, combining them can increase the likelihood of experiencing certain minor side effects, as noted in a 2023 study.

Potential Side Effects

Gastrointestinal Issues: Taking the combination on an empty stomach might increase the risk of nausea, which was one of the adverse events reported in the 2023 study.
Headaches: While caffeine can treat some headaches, withdrawal can cause them. Furthermore, some individuals in the aforementioned study reported headaches after taking the combined supplement.
Dizziness: Mild dizziness was also noted as an adverse event in some participants.
Increased Heart Rate/Blood Pressure: The stimulant effect of caffeine can increase heart rate and blood pressure. Those sensitive to caffeine or with pre-existing heart conditions should be cautious and consult a doctor before combining supplements. For many, the vasodilating effects of citrulline are not enough to completely counteract caffeine's impact on heart rate.

Practical Application and Timing

For those who wish to combine coffee with citrulline, timing is key to maximizing potential benefits while minimizing side effects. It's best to consume the mixture about 30 to 60 minutes before your workout. This allows time for the supplements to be absorbed and for their active effects to peak around the start of your training session.

Best Practices for Combining:

Start Low and Go Slow: Begin with a conservative dose of citrulline (e.g., 6-8 grams of citrulline malate) and a moderate amount of coffee to see how your body reacts. Do not exceed recommended dosages.
Stay Hydrated: Proper hydration is crucial, especially when consuming stimulants like caffeine. Drink plenty of water throughout the day.
Monitor Your Body: Pay close attention to how you feel. If you experience significant side effects, consider separating the intake of coffee and citrulline or reducing your dose.
Consider Your Workout Type: The benefits of citrulline for blood flow are most noticeable during endurance and resistance training where sustained performance and pumps are key. Caffeine's stimulant effects are beneficial across many exercise types.

Comparison: Coffee vs. Citrulline vs. Combined


Feature	Coffee (Caffeine)	Citrulline	Combined (Coffee + Citrulline)
Mechanism	CNS stimulant, blocks adenosine receptors	Increases nitric oxide, promotes vasodilation	Combines CNS stimulation and vasodilation
Primary Effect	Increased energy, alertness, focus, and reduced perceived effort	Enhanced blood flow, reduced muscle soreness, muscle pumps	Increased energy and enhanced blood flow, potentially leading to better pumps
Synergy	N/A	N/A	Unlikely to provide additional performance benefits for strength/endurance beyond caffeine alone
Performance Impact	Proven to enhance muscular strength and endurance	May improve endurance and recovery	Offers the performance benefits of caffeine with potential blood flow support
Common Use	Pre-workout energy boost, daily consumption	Pre-workout for pumps and performance, general cardiovascular support	Pre-workout for a mix of energy and pump enhancement
Side Effects	Jitters, insomnia, increased heart rate	Generally minimal, but high doses may cause GI issues	Increased risk of mild side effects like nausea or headache compared to either alone

Conclusion

In short, the answer to "Can I drink coffee with citrulline?" is yes, it's generally safe for most healthy individuals. This combination is a common practice, particularly in pre-workout regimens. While research has shown that the added effect on exercise performance may not be significantly greater than taking caffeine alone for some metrics, the benefits of improved blood flow from citrulline and heightened alertness from caffeine can still provide a useful boost. The key is to pay attention to your body's response, start with a lower dosage, and consider potential side effects like mild gastrointestinal discomfort. Always consult a healthcare provider before starting a new supplement routine, especially if you have pre-existing medical conditions or are sensitive to stimulants like caffeine. For a deeper dive into the science behind this combination, you can review relevant research studies on platforms like PubMed.

Frequently Asked Questions

Yes, for most healthy individuals, it is considered safe to mix coffee and citrulline. No major drug interactions between caffeine and citrulline have been found.

For optimal performance, it is best to take coffee with citrulline approximately 30 to 60 minutes before your workout. This timing allows the active compounds to be absorbed and to take effect during your exercise.

Some studies have found that combining caffeine and citrulline malate did not provide significant additional performance benefits for muscular strength and endurance compared to taking caffeine in isolation.

Yes, some people may experience mild side effects like nausea, headaches, or dizziness when combining coffee and citrulline, especially at higher doses. It is advisable to monitor your body's reaction and start with a conservative dose.

This is a subject of ongoing research. While citrulline promotes vasodilation and caffeine can cause vasoconstriction in some areas, the overall effect during exercise can be a balance. It is not confirmed that citrulline completely counteracts all of caffeine's vasoconstrictive properties.

Citrulline enhances blood flow by increasing nitric oxide production, which can lead to reduced muscle soreness, faster recovery, and better endurance.

Coffee's caffeine content acts as a stimulant, increasing alertness, focus, and energy levels. It can also reduce the perception of effort, allowing for more intense or longer workouts.

Yes, citrulline powder can be mixed into coffee or other beverages. However, be mindful that it can alter the flavor of your drink. Some people prefer taking their supplements separately.