Side Effects of Paraxanthine

Paraxanthine is advertised as a "cleaner" and milder stimulant than caffeine. But any methylxanthine has its side effects. The editorial team analyzed what is known about the tolerability of paraxanthine, where the data is direct, and where one has to rely on the pharmacology of caffeine.

General safety profile

A conversation about the side effects of paraxanthine is worth starting with the main point: it is a methylxanthine, and its tolerability profile is broadly similar to caffeine. Paraxanthine blocks adenosine receptors, stimulates the sympathetic nervous system and affects the heart and blood vessels. So the undesirable effects are mostly the same as those from an excess of coffee.

However, there are nuances. Paraxanthine bypasses the first stage of caffeine metabolism and is not accompanied by the formation of theobromine and theophylline. Advocates of the substance believe this makes its tolerability better. There are still few direct comparative safety studies that would unambiguously confirm this.

As with any stimulant, the risk of side effects depends on dose, individual sensitivity, health status, time of intake and simultaneous use of other stimulants. The same amount that is imperceptible for one person may cause palpitations and insomnia in another.

Below we examine the side effects by body system, relying on paraxanthine studies where they exist, and on the well-studied pharmacology of caffeine where direct data is lacking.

Nervous system and sleep

The most frequent adverse reactions to methylxanthines concern the nervous system: restlessness, irritability, hand tremor, a feeling of being "overexcited." The study by Orrú and colleagues in rats showed that paraxanthine, unlike caffeine, did not increase anxiety-like behavior. This is an interesting result, but in humans it requires confirmation.

Sleep disturbance is probably the most significant side effect for athletes. Adenosine is one of the key regulators of drowsiness, and blocking it in the evening delays falling asleep and worsens sleep depth. Since paraxanthine is eliminated within a few hours, taking it in the afternoon may affect nighttime rest.

Headache can arise both from an excess of the stimulant and from its abrupt cessation. Caffeine withdrawal syndrome is a documented phenomenon with headache, fatigue and reduced concentration. Whether it occurs with regular paraxanthine intake and how pronounced it is has not been separately studied, but by mechanism it is entirely possible.

In people with anxiety or panic disorders, even moderate doses of methylxanthines can provoke a flare-up. For them, promises of "stimulation without anxiety" are no reason to experiment without a doctor.

Heart and blood vessels

Cardiovascular effects are the most important argument against the notion of paraxanthine as a "completely mild" stimulant. The study by Benowitz and colleagues (1995) directly compared paraxanthine and caffeine in humans and showed that both substances raise blood pressure and the plasma concentration of adrenaline.

In healthy people such changes are usually moderate and temporary. But for those who have hypertension, arrhythmias or ischemic heart disease, the reaction can be far more dangerous. Additional load on the heart during intense exercise raises the stakes even further.

A racing heartbeat and a feeling of "skipped beats" in the heart are grounds to stop intake and consult a doctor. One should not try to "tough out" these symptoms or lower the dose at random without finding out the cause.

A separate mention should be made of combining it with other sympathomimetics: synephrine, yohimbine, some cold remedies with decongestants. Such combinations sum up the effect on blood pressure and heart rhythm.

Digestion, urination and overdose

Methylxanthines can irritate the stomach lining and stimulate acid secretion. Hence heartburn, nausea or discomfort, especially when taken on an empty stomach. Paraxanthine in capsules is free of the acidic components of coffee, but the stimulant itself can affect digestion.

Increased intestinal motility is another familiar effect of coffee. For runners and other endurance athletes this can be a practical problem during competition. Your reaction to paraxanthine is worth checking in training, not on race day.

A mild diuretic effect is also characteristic of methylxanthines. At moderate doses it usually does not cause dehydration in people accustomed to coffee, but in heat or during prolonged exercise it is important to monitor fluid intake.

Signs of methylxanthine overdose include severe palpitations, vomiting, agitation, tremor, and in severe cases convulsions and arrhythmias. Such a state requires emergency medical care. It most often occurs when taking concentrated powders, where it is easy to make a dosing mistake.

Interactions and how to reduce risks

The blood concentration of paraxanthine is determined by the activity of the liver enzyme CYP1A2, which also participates in its subsequent metabolism. Drugs that inhibit this enzyme (for example, fluvoxamine, ciprofloxacin) significantly slow the elimination of caffeine, and it is logical to expect a similar effect on paraxanthine.

Conversely, smoking accelerates the metabolism of methylxanthines. A person who has quit smoking may suddenly notice that their usual stimulant dose acts more strongly and longer. This effect is described in detail for caffeine in the review by Nehlig.

Oral contraceptives and pregnancy also slow the metabolism of caffeine. In such situations, doses that were previously well tolerated can cause side effects.

To reduce the risk of adverse reactions, the editorial team advises following simple rules:

• start with a minimal serving and do not increase it without need;
• account for all caffeine and stimulants consumed during the day;
• do not take paraxanthine in the afternoon if sleep is disrupted;
• discuss intake with a doctor if you have chronic conditions or take medications.

These rules are simple, but it is precisely they that cut off most of the problems associated with stimulants.

Editorial conclusions

The side effects of paraxanthine are mostly the same as those of caffeine: restlessness, sleep disturbance, headache, stomach discomfort. There is still little data on better tolerability in humans.

Paraxanthine raises blood pressure and adrenaline levels, so people with cardiovascular diseases need special caution and a doctor's consultation.

Drugs that inhibit CYP1A2, pregnancy and quitting smoking can enhance the action of paraxanthine. Concentrated powders carry a risk of accidental overdose.

To complete the picture, we recommend our articles "Who Should Not Take Paraxanthine," "How to Take Paraxanthine" and "Side Effects of Theacrine."

References

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2. Orrú M, Guitart X, Karcz-Kubicha M, et al. Psychostimulant pharmacological profile of paraxanthine, the main metabolite of caffeine in humans. Neuropharmacology. 2013;67:476–484.
3. Nehlig A. Interindividual differences in caffeine metabolism and factors driving caffeine consumption. Pharmacol Rev. 2018;70(2):384–411.
4. Arnaud MJ. Pharmacokinetics and metabolism of natural methylxanthines in animal and man. Handb Exp Pharmacol. 2011;(200):33–91.
5. EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Scientific opinion on the safety of caffeine. EFSA J. 2015;13(5):4102.
6. Wikoff D, Welsh BT, Henderson R, et al. Systematic review of the potential adverse effects of caffeine consumption in healthy adults, pregnant women, adolescents, and children. Food Chem Toxicol. 2017;109(Pt 1):585–648.
7. Xing D, Yoo C, Gonzalez D, et al. Dose-response of paraxanthine on cognitive function: a double blind, placebo controlled, crossover trial. Nutrients. 2021;13(12):4478.