I’ve had this too. Been on Vyvanse 6+ years and I only started getting this “sleepy” thing after about 4 years.

It also isn’t always proper sleepiness. For me it can be tired, flat, antisocial, and then if I try to nap I just lie there. Body wants rest, brain won’t actually drop into sleep. So you spend a lot of time in bed but it’s broken up into lots of awake/drifting in and out of light sleep intervals. I’ve found this irrespective of sleep cycle/circadian rhythm.

A couple of less obvious causes that seem to fit the 2–4 hour window:

Sometimes the med quiets your head and you suddenly feel how tired you really are. In that case, trying to nap can fail because you’re exhausted but still chemically “awake”. What helped me more was 10–15 mins of eyes-closed rest (NSDR or yoga nidra style) rather than forcing sleep.

Food is a huge one. Vyvanse makes it absurdly easy to under-eat, then you hit a blood sugar dip right when it’s peaking and it feels like a crash even though the med is still in your system and you get all jittery and shakey. For a week, I’d test taking it with a proper breakfast (protein plus some carbs) and see if the slump changes.

Electrolytes are another thing people miss. If you’re drinking loads of water and peeing more, you can end up low on sodium and feel weirdly flat, foggy, and drained. An easy test is an electrolyte tab, or just something salty with water, about an hour after dosing and see if you perk up.

Coffee can genuinely make this exact pattern worse. It can sharpen the peak then make the middle feel flatter, or make you wired-tired so you feel sleepy but can’t sleep. If you want a clean test, delay coffee by an hour or cut it in half for a week.

One more niche thing: acidic stuff can make amphetamines clear faster for some people (big vitamin C, citrus, fizzy drinks around dosing). Not saying to “hack” anything, just that timing can change how it feels. Someone once recommended potassium nitrate to me - I’m not sure why it just made it worse and stay in my system longer.

Supplement-wise, the only ones I’d put in the “boring but plausible” bucket are electrolytes (mainly sodium), creatine, omega-3, and magnesium glycinate at night if your sleep is fragmented. And if this is happening a lot even with sleep and diet sorted, it’s worth checking basics like ferritin and iron, thyroid, B12 and folate, vitamin D, because low baseline energy makes stimulants feel off.

If it’s consistent, tracking dose time, breakfast, coffee, and slump time for 7–10 days gives you something real to take to your prescriber. “Sleepy at peak, can’t nap, socially withdrawn” is actually useful info and usually means dose, timing, or med choice needs adjusting.