There's limited evidence for prescription amphetamines being more effective in high doses, Moran said. A clinical study by the U.S. Food and Drug Administration (FDA) found that doses exceeding 20 mg per day didn't provide additional benefits.
The FDA doesn't specify a maximum recommended dose on approved labels.Additionally, only amphetamines prescribed for children contain the statement that only in rare cases will it be necessary to exceed a total of 40 mg per day, Moran said. There is no such upper limit label for adults that doctors can adhere to, he added.
Recent studies show a difference in the risk profiles of two commonly prescribed ADHD medications. Amphetamines, such as Adderall, have been linked to an increased risk of psychosis and mania, while methylphenidates, like Ritalin, do not appear to carry this risk.
According to the study, both types of stimulants work by increasing dopamine levels in the brain, but amphetamines cause four times more dopamine release than methylphenidates, while methylphenidates are more effective at preventing dopamine reabsorption.
The current study, consistent with previous research, found that the risk of psychosis and mania was present only in patients taking amphetamines, not in those using methylphenidate.
"Adderall is more potent but also has more side effects and a greater risk of triggering mania and psychosis," Dimitriu said. "Ritalin generally is more gentle and easier to tolerate with fewer risks of adverse reactions," he added.
While the study does not establish causality, researchers hypothesize that the higher levels of dopamine released by amphetamines may be a key factor. This higher dopamine release mimics the increased dopamine levels seen in people with psychotic disorders, potentially explaining the stronger association between amphetamines and these mental health conditions.
"It does not surprise me that amphetamine presents with a higher risk of psychosis given its binding affinity and effects on serotonin and dopamine concentrations," Oliver Grundmann, a clinical professor in pharmaceutical chemistry and clinical toxicology at the University of Florida College of Pharmacy, told The Epoch Times via email. "The mechanism of action for amphetamine is also different from Ritalin, so it does make sense to see a difference."