Has he had a sleep study done to rule out sleep apnea? He could try Trazodone, which is commonly prescribed for insomnia as one side effect is sleepiness. He could also try a low dose of melatonin. I take 2.5mg melatonin 15 minutes before bed along with 50-75mg trazodone. I also take a sleep gummy with 10mg CBN and 5mg THC (Minny Grown brand called Highbernate). Take with a light snack (I eat yogurt) as it helps both the Trazodone and CBN last longer in your system. Another drug prescribed for sleep is Mirtazapine, about 7.5 mg. It has a longer half-life than Trazodone so might make the sleepiness last into the next day.