What Medications Affect VO2 Max and How?

Dozens of commonly prescribed medications can shift your VO2 max, the maximum rate at which your body uses oxygen during intense exercise, either by changing how your heart pumps blood, how your muscles extract oxygen, or how your body adapts to training over time. Beta-blockers produce the most dramatic acute reductions, but the list extends well beyond them to include diabetes drugs, cholesterol medications, diuretics, stimulants, and even over-the-counter antihistamines. The effects range from a modest blunting of fitness gains over months of training to an immediate and measurable drop in peak performance, and understanding which drugs do what can help you make sense of a fitness test result or a workout that feels harder than it should.

Beta-Blockers Have the Largest and Most Consistent Effect

If you take a beta-blocker and feel like you hit a ceiling during hard exercise, you are not imagining it. These drugs work by blocking the adrenaline receptors on your heart, which directly caps how fast your heart can beat. Since cardiac output (heart rate multiplied by the volume of blood pumped per beat) is the single biggest driver of VO2 max, lowering the ceiling on heart rate pulls VO2 max down with it. In a controlled crossover study, propranolol reduced maximal heart rate to roughly 90 beats per minute at peak effort compared to about 130 in the placebo condition, and measured VO2 max dropped from about 50 to 48 ml/kg/min even in healthy young subjects.¹ That may sound like a small absolute drop, but in people who are less fit or who have heart conditions to begin with, the proportional hit is steeper.

Not all beta-blockers are created equal here. Non-selective beta-blockers, the kind that block both beta-1 receptors in the heart and beta-2 receptors elsewhere, impair exercise performance more than beta-1-selective ones at the same degree of heart rate reduction. The extra impairment comes from blocking beta-2 receptors in muscle and liver, which throttles glycogen breakdown and limits the fuel available during exercise.² A study comparing the selective beta-blocker nebivolol with the non-selective carvedilol at altitude found that peak VO2 was better preserved with nebivolol (a drop of about 23%) than with carvedilol (a drop of about 38%).³

Your body does try to compensate. When heart rate is capped by a beta-blocker, the heart stretches more between beats and pushes out a larger volume of blood with each contraction. Research in healthy men taking propranolol found that cardiac output at maximal exercise was maintained at roughly 20 liters per minute, similar to the unmedicated state, because stroke volume increased to offset the slower heart rate.⁴ This compensation is real but incomplete. The overall ceiling is still lower, and exercise at a given intensity feels considerably harder.

Other Blood Pressure Drugs Are More Forgiving

If beta-blockers sit at one extreme, calcium channel blockers sit near the other. Drugs like verapamil, diltiazem, and nifedipine lower blood pressure through different mechanisms, and the evidence consistently shows that VO2 max and endurance performance are not impaired following their use.⁵ Verapamil-type calcium blockers do lower exercise heart rate by about 10 to 15 beats per minute, but unlike with beta-blockers, this does not translate into a measurable reduction in peak oxygen uptake. A training study in men with hypertension found that those taking diltiazem improved their VO2 max with exercise training just as well as those on placebo, while the group taking propranolol did not see the same gains.⁶

ACE inhibitors and angiotensin receptor blockers (ARBs) fall somewhere in the middle, and the picture depends on what you are measuring. In a placebo-controlled study of healthy subjects undergoing aerobic training, ACE inhibitor treatment did not dampen the VO2 max improvement. Both groups gained about 13% in aerobic capacity over the training period.⁷ However, a broader review of the evidence suggests ACE inhibitors may blunt some of the specific physiological building blocks of fitness, like the expansion of total hemoglobin mass and the accrual of lean muscle mass, even if the VO2 max number itself holds up. There are also signs that women may experience a more pronounced inhibition of aerobic adaptations from ARBs compared to men.⁸ In heart failure patients with preserved ejection fraction, a meta-analysis of randomized trials found that renin-angiotensin system inhibitors did not significantly improve exercise capacity measures like six-minute walk distance.⁹

Metformin Blunts the Gains You Get from Training

Metformin is one of the most prescribed drugs on the planet, and its interaction with exercise is more interesting than most people realize. It does not acutely lower your VO2 max the way a beta-blocker does. Instead, it interferes with the adaptive process: the mitochondrial improvements your muscles normally make in response to endurance training are partly blocked. In older adults undergoing aerobic exercise training, metformin attenuated the increase in VO2 max and abrogated the exercise-mediated increase in skeletal muscle mitochondrial respiration.¹⁰

The magnitude of this effect can be substantial. A prospective study in men and women with elevated blood sugar found that metformin users who exercised improved their VO2 max by about 13%, while those who exercised without metformin gained about 25%, roughly cutting the fitness benefit in half.¹¹ This does not mean you should stop metformin to train harder. The drug provides clear metabolic benefits that may outweigh the fitness trade-off, especially for people managing type 2 diabetes. But it does mean that if you are on metformin and feel like your cardio progress is frustratingly slow, the medication is a plausible contributor.

Statins May Undermine Mitochondrial Fitness

Statins are another class of widely prescribed drugs where the exercise interaction is real but poorly understood by most patients. Research has shown that simvastatin at a standard dose diminished the increase in skeletal muscle enzyme activity and whole-body aerobic capacity that normally occurs with 12 weeks of endurance training in people who were overweight. High-dose atorvastatin has also been reported to progressively reduce skeletal muscle mitochondrial oxidative capacity even without a concurrent exercise program.¹² The mechanism appears to overlap with statins’ known tendency to cause muscle-related side effects: by interfering with mitochondrial function in skeletal muscle, they may limit the machinery that turns oxygen into energy during exercise.

The evidence here is still conflicting, and not every study has found the same effect. But for people who exercise regularly, take a statin, and notice that their fitness plateau seems harder to break through than expected, this is a documented possibility worth discussing with a prescribing clinician.

SGLT2 Inhibitors in Heart Failure

SGLT2 inhibitors, a newer class of diabetes and heart failure medication, present a different and more encouraging story. A systematic review and meta-analysis found that patients with heart failure who received SGLT2 inhibitor treatment experienced a meaningful increase in peak VO2 of about 1.6 ml/kg/min compared to controls, along with a modest improvement in six-minute walk distance.¹³ In the context of heart failure, where peak VO2 values are often quite low, a gain of that size is clinically significant.

That said, not every study has found the same benefit. A study specifically in advanced heart failure patients found that adding an SGLT2 inhibitor to already-optimized medical therapy did not produce a statistically significant improvement in peak VO2 after one year of follow-up.¹⁴ The discrepancy likely reflects disease severity: in less advanced heart failure, the drugs may have more room to help, while in patients who are already severely limited, the marginal benefit on exercise capacity is harder to detect.

Diuretics and the Plasma Volume Problem

Diuretics reduce blood volume, and blood volume is one of the key variables your body expands in response to endurance training. When healthy untrained men took a common diuretic combination (triamterene plus hydrochlorothiazide) while simultaneously doing short-term exercise training, their plasma volume remained significantly reduced, roughly 8% below baseline, despite the training stimulus that would normally expand it.¹⁵ Less blood volume means less blood returning to the heart with each beat, which limits stroke volume and therefore cardiac output. For endurance athletes, this is a meaningful handicap, and it also explains why diuretics are banned in many sports: they can mask other substances through dilution, but they also carry a direct physiological penalty.

Stimulants and ADHD Medications

The relationship between stimulant medications and VO2 max is more complex than you might guess. A large propensity-matched study of people taking prescription stimulants (predominantly for ADHD) found no significant difference in estimated VO2 max compared to non-users. Peak heart rate was actually lower in stimulant users during exercise testing, and stimulant use was associated with over three times the odds of chronotropic incompetence, meaning the heart failed to reach the expected rate for the person’s age.¹⁶ That finding is somewhat paradoxical: stimulants raise resting heart rate, yet during maximal exercise the heart rate ceiling appears to be lower in chronic users.

There is a separate question about whether stimulants help you exercise longer at a given intensity even if they do not change VO2 max itself. Modafinil, a wakefulness-promoting agent sometimes grouped with stimulants, significantly extended time to exhaustion at 85% of VO2 max compared to placebo, with subjects lasting about 18 minutes versus 16 minutes.¹⁷ The mechanism likely involves altered perception of effort rather than a genuine change in oxygen delivery. A systematic review of ADHD medications found that while some stimulants changed perceived exertion during exercise, the overall effects on traditional performance metrics were inconsistent.¹⁸

SSRIs and Antidepressants

For the millions of people on selective serotonin reuptake inhibitors, the exercise news is mostly reassuring. A controlled study of fluoxetine (Prozac) found no effect on VO2 max or time to exhaustion at high intensities. The only measurable changes were a slight reduction in maximal voluntary contraction acutely and a small decrease in minute ventilation during the chronic phase, neither of which translated into a meaningful performance difference.¹⁹

In older adults, the relationship between psychotropic medications and fitness is more nuanced but runs in a direction that is hard to interpret causally. A large study of community-dwelling older adults found a curvilinear association: as peak oxygen uptake increased toward about 40 ml/kg/min, the use of psychotropic medications and antidepressants decreased. Above that fitness level, the pattern reversed slightly, though the association was strongest at the lower end of the fitness continuum.²⁰ This is likely a reflection of fitter people needing fewer medications rather than the medications lowering fitness.

Inhaled Bronchodilators for Non-Asthmatic Users

Salbutamol (albuterol) inhalers are sometimes used by athletes who do not have asthma, hoping the bronchodilator effect will boost oxygen delivery to muscles. The evidence says it does not work that way. In elite non-asthmatic athletes, a therapeutic dose of inhaled salbutamol produced no significant change in VO2 max and no ergogenic benefit.²¹ In people who already have normal airway function, opening the airways further does not meaningfully increase oxygen transport, because the bottleneck during maximal exercise is not in the lungs. Asthma sufferers, of course, are a different story: relieving bronchospasm restores normal breathing and allows them to reach the VO2 max their cardiovascular system can support.

Antihistamines and Post-Exercise Blood Flow

This is one of the more surprising entries on the list. Histamine, the same molecule you try to suppress during allergy season, turns out to play a significant role in the body’s response to exercise. Research has shown that histamine is released within working skeletal muscle during exercise and that taking antihistamines modifies more than 25% of the genes that normally respond to a bout of physical activity.²² Histamine contributes to the sustained increase in blood flow to muscles after exercise, which is thought to support nutrient delivery and recovery. By blocking that response, antihistamines may not change your VO2 max number on a single test, but they could alter the downstream training adaptations that improve it over time. The research on this is still early, and nobody is suggesting you skip your allergy medication during training season. But it is a reminder that exercise physiology involves molecular signals most people never think about.

Erythropoietin and Oxygen-Carrying Capacity

Erythropoietin (EPO) sits on the opposite end of the spectrum from everything discussed above. Rather than reducing VO2 max, it enhances it by increasing the number of red blood cells in the bloodstream, directly boosting how much oxygen the blood can carry. Prolonged treatment with recombinant EPO has been shown to increase VO2 max by about 6 to 7% under normal conditions, with even larger gains under moderate altitude-like conditions where the body is already oxygen-limited, reaching 14 to 17% improvements at moderate simulated altitudes.²³ EPO is banned in competitive sports for exactly this reason: the performance benefit is unambiguous. In clinical medicine, EPO or similar drugs are prescribed for anemia due to chronic kidney disease or chemotherapy, and in those patients the increase in exercise capacity is a therapeutic goal, not doping.

One wrinkle: EPO does not work at all altitudes. Under conditions of severe oxygen deprivation, the extra red blood cells do not help because the lungs cannot load them with enough oxygen in the first place. The benefit scales with how much oxygen is available in the air, peaking at moderate elevations and disappearing at extreme ones.

Acetaminophen and Pain Perception During Exercise

Acetaminophen (paracetamol) does not change your VO2 max in any mechanistic sense, but it may change how hard you can push yourself. Research into its effects on running economy and time-trial performance in collegiate distance runners has explored whether reducing pain perception during exercise allows athletes to sustain higher efforts.²⁴ The rationale is straightforward: if exercise hurts less, you can tolerate a higher fraction of your true physiological maximum, which shows up as a better performance even though the underlying cardiovascular ceiling has not changed. The practical effect appears small and varies between individuals, but it illustrates an important distinction. Some medications change the physiology that determines VO2 max, while others change the perception of effort that determines how close you get to it.