It’s part of routine healthcare prevention check ups to ask patients about caffeine intake. Typically, that means asking how much coffee, tea and soda the patient drinks. We now also ask about energy drinks, since consumption of energy drinks is on the rise among adolescents and adults.

This got me wondering what actual amounts of caffeine are safe to consume, and how much is too much. I’ve also wondered whether certain populations of patients are at higher risk for adverse effects from caffeine than others. 

Some of my patients consume significant quantities of caffeine daily to improve their sustained focus. When I completed ADHD questionnaires, these patients very often met diagnostic criteria for the disorder. I wondered whether there were studies evaluating benefits of caffeine for these patients.

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Caffeine is the most highly consumed psychoactive substance in the world. Caffeinated tea or coffee is consumed daily by up to 92% of American adults. Up to 77% of children consumes caffeine in soda, snacks with chocolate, tea and some medications. Research suggests that healthy adults can probably safely consume about 400 mg of caffeine per day. But that amount does increase norepinephrine levels and systolic blood pressure by about 6%. As such, the risk of having a cardiac event is likely increased as well. About 400 mg of caffeine translates to approximately two to four cups of brewed coffee (specialty coffees can contain higher amounts of caffeine), five to 10 caffeinated sodas, 16 ounces of energy drinks or two energy shots.

The content of caffeine in tea is variable—up to 100 mg per cup, depending on the type of tea and how long the tea leaves are steeped. High quantities of caffeine are also found in certain over-the-counter medications.  These products are readily available to adolescents, even though the American Academy of Pediatrics advises no more than 100 mg of caffeine per day for teens and none for children. Amounts above 400 mg daily can cause insomnia, anxiety, motor restlessness, irritability, gastrointestinal distress/gastritis, tachycardia and muscle tremors.

Certain populations do seem to be more at risk for adverse effects from caffeine. These include patients with preexisting hypertension and other cardiovascular conditions (such as arrhythmia) and, interestingly, patients with generalized anxiety disorder (GAD) and panic disorder. People with GAD appear to be significantly more prone to experiencing elevated anxiety symptoms or having an adverse response to caffeine than those without an underlying anxiety disorder.

As far as how people with ADHD respond to caffeine, multiple studies have shown varied results. In general, low doses of up to approximately 50 mg per day—or 1-2 mg/kg/day—in prepubertal children appears to improve performance for some learning tasks, but not all. Performance for some learning tasks was also improved in college-aged students with ADHD. In the younger children, motor activity increased, while both groups experienced feelings of nervousness. It seems the jury is still out on benefits vs harms of caffeine, and I won’t be recommending it as a treatment intervention. However, I do wonder if the positive effect of some improved learning performance justifies caffeine use in this population.

Of course, tolerance can quickly develop for those who consume caffeine regularly and in high quantities. There is the well-known withdrawal syndrome, which includes headache, irritability, nervousness and fatigue. Thankfully, patients can be reassured that the symptoms are short lived, usually lasting only a few days, and can be mitigated by cutting back gradually.

My general practice continues to recommend very little to no caffeine intake, even for adults, especially if it is consumed in sugary drinks. Regarding benefits for specific medical or psychiatric conditions, that is still unclear.

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