Many of us will be familiar with feelings of sluggishness and lethargy in the afternoon, but for those with obstructive sleep apnea (OSA), the problem is more severe.

Fortunately, researchers have now identified a drug that offers a good chance of helping. And no, it doesn't come in espresso form.

Excessive daytime sleepiness (EDS) for people who have OSA can severely affect daily life. It means having overwhelming urges to sleep at inappropriate times – while driving or eating, for example – and often struggle to complete simple tasks.

While a positive airway pressure (PAP) mask is standard issue for those with OSA, and can help support the lungs with compressed air at night, it doesn't always eliminate EDS. As a result, experts are working to identify drugs that could lend a hand.

"The most important thing that people with OSA should do is use their PAP machine, but if they are still sleepy there are options in the form of medications that can reduce their tiredness," says resident physician in internal medicine Tyler Pitre, from McMaster University in Canada.

Pitre and his colleagues reviewed 14 previous clinical trials involving 3,085 people with OSA and EDS, looking at the comparative effectiveness of three anti-fatigue medications: solriamfetol, armodafinil-modafinil, and pitolisant. All three were more effective than placebos at combating EDS, to varying degrees.

Combining the data for the 14 trials, the team found that solriamfetol offered the biggest statistical difference over a placebo in terms of wakefulness. The evidence wasn't quite as concrete for armodafinil-modafinil and pitolisant, which "probably improve" some, but not all, measures of wakefulness after a month of use. The statistics also showed that side effects could be an issue with armodafinil-modafinil and solriamfetol, though patients were more likely to stop using the former.

While it's difficult to summarize findings across multiple trials, the comparison does show solriamfetol's effects out in front, possibly as a result of increases to levels of norepinephrine (readying the body for action) and dopamine (linked to pleasure and motivation) in the brain.

The researchers say solriamfetol's pros and cons are worthy of further investigation, particularly in terms of the longer term effects on people who take it because there is little evidence on long-term use. And and it's not just those with OSA and EDS who might find solriamfetol and these other drugs helpful.

"It would be interesting to see how effective these anti-fatigue medications will be for treating related illnesses such as chronic fatigue syndrome and long COVID, now that we know they work for a similar condition," says assistant anesthesia professor Dena Zeraatkar, from McMaster University.

But there is still a lot we don't know about long COVID or chronic fatigue, and any treatment for them should ideally get at the underlying causes, of which there are many.

Two of the drugs studied are already prescribed for OSA and EDS, with pitolisant still under review by the US FDA. Which drug a doctor prescribes depends on a range of factors including the patient's personal health profile. However, this is the first time that these treatments have been compared against each other in this way.

With side effects potentially an issue – solriamfetol has been linked to an increase in blood pressure for example – care needs to be taken. That said, with as many as a billion people globally affected by OSA, there's clearly an urgent need for better treatments to be found.

"Fifteen to 30 percent of people in North America have a diagnosis of OSA and the prevalence could be much higher as many others are undiagnosed," says Pitre.

"Many people have symptoms as the condition is highly associated with obesity, which affects a large and increasing number of people in Canada, the United States and other high-income countries."

The research has been published in the Annals of Internal Medicine.