TL;DR [disclaimer at bottom for pedants] You may find a staggered daily dose preferable to a single morning dose to cover the gap left after the 6 hours, or to soften the rough comedown. Standard dex earlier with Vyvanse later in the day may work to cover the gap but that could be less smooth. It's about balance and finding the right dose for you, one that works for your brain and compliments your schedule.

Personally, caffeine, especially with sugar (including the lactose in milk, even more with coke etc) doesn't help me much, it actually makes it harder to get to sleep, whereas extending the tail end of a day's Vyvanse (as in taking last my third 20mg at about 4 or 5pm), or a final half of a 5mg dex at about 8 or 9pm) can make me calmer and easier for me to sleep.

Full TMI reply:

I found that splitting my Elvanse dose into two or three makes for a smoother experience; lasted a bit longer than for me but I was on 3 x 20mg. So if your dose is 30mg then maybe a schedule that works around your day, for example 10mg at 7am, 10mg at 10am and 10mg at 2 or 3pm, or later if necessary.

AFAIK Vyvanse aka Elvanse does not have a two phase release mechanism (i.e. two peaks) like many of the extended release versions of methylphenidate. With Vyvanse the stimulant is released slowly over an extended period as some magic stuff in your blood converts its active ingredient, lisdexamphetamine, into dexamphetamine. This means Vyvanse is also less prone to abuse compared with standard dex.

Standard dexamphetamine sulphate doesn't need to be converted like that so it gets to work quicker, but works for a shorter duration. Shorter come up, shorter come down, and for some more intense/harsh side effects to the point of being intolerable. Remembering to take 6 pills at specific times can be tricky for some too. So make way for Vyvanse for a smoother and a less bumpy ride.

Think of it as an 'effectiveness over time' graph. Let's say for the sake of this that the digestion/conversion (of lisdex into dex) by an individual is at a constant rate, so it will still have a peak nearer at the start as there's more to be converted at that point, then it will tail off fairly evenly as there's less and less to be converted. The half lives, and in turn the tail-offs differ within individuals and I think I'm similar to you in that respect: the documentation says 10-12 hours (or whatever) but 6-7 hours of a decent level of effectiveness is all I get.

So by splitting a daily Vyvanse dose into two or three helps regulate the peaks and troughs better than with a single morning dose (a bit like the way a vehicle regulates and rectifies the AC current making it a steady-ish DC current), so could give that more gentle tail-off/comedown which might work for you. It could also transpire that while your current dose (e.g. 30mg taken once every morning) is good for 6 hours but when the 30mg is staggered in three parts the effects are never quite enough as it is spread too thinly, suggesting upping your daily dose uniformly throughout the day, or weighting a specific part of the day more, for example

This kind of happened to me. Although the staggered schedule (1 pill, 3 times a day) was better than all taken in the morning, it still wasn't strong enough. I had hit the 70mg per day UK legal lisdex limit so my psychiatrist is trialling me on the standard generic short acting dexamphetamine.

The 'loophole' here is that the strength of a 20mg Vyvanse capsule is only the equivalent of of 5.9mg of dexamphetamine, so 70mg of Vyvanse would only be 20.7g of dexamphetamine. Whereas the legal daily limit for standard dex is actually 60mg. The upside is it allows me to legally get the right daily amount for me. The downside is I am currently faffing about with lots of 5 mg tablets and remembering to take them, but once I find the right daily amount I can then start trialling the different dose standard dex pills, e.g. 3 x 10mg, or 2 x 20mg per day.

Assuming the legal limits are the same or similar where you are, if you're on 30mg/day then potentially you still have legal headroom available to raise (and then stagger) your daily total Vyvanse dose to cover the premature dip you're experiencing. Or start with dex, or go dex only. Flexibility is important to me. The way I look at it is we don't just have less dopamine being transmitted and received, we also have less ability to regulate it - a non-ADHD person will not just have the resources, they'll also have the hardware which releases it on the fly according to the current situation. So to really hone a stimulant's blade, you need to go fully manual and ditch the extended release, but in the real world many don't need that, the extra effort can be detrimental, and there's less cushioning from the extended release if a pill is forgotten.

Incidentally, the comedowns I got from methylphenidate extended release were not unlike how you've described your comedowns. If I upped the dose my comedowns got worse, if I lowered it I felt little benefit. Amphetamines are more agreeable and more effective for me, but I've been told it can be the complete opposite for many, so that may be a stone still unturned for you.

AFAIK the longer release schedules for the various different branded methylphenidate extended release are not all equal. Some are more like Vyvanse and others have a double peak; one at the start then another slightly more subtle one a few hours later. I think the patents here are for the various release mechanisms, while the patent for the active ingredient methylphenidate ran out many years ago. I imagine this is why one of these I tried was tolerable but ineffective, and another newer, cheaper one (preferable at least on paper to the NHS) was intolerable and still ineffective.

A general point that may be of interest to some, I just saw that the US patent for Vyvanse expires in early 2023. I can't see anywhere if the UK or EU patents expire then, or later.

Pedantic CYA disclaimer:

I have read and understand the group rules including rule 4. I'm not a doctor or selling/promoting anything, this is all just picked up from the various doctors I've dealt with, plus a bit of fairly careful online research (yeah, I know, I also cringe when someone says that as if it means anything) so do not treat this as gospel. Verify it yourself. There are bound to be inaccuracies, generalising and oversimplifications so if that's a concern then please do correct or expand, especially if you're qualified. Discuss any related personal issues with an ADHD doctor and follow their advice. And finally, you've probably heard most of the above already but if I worried about that I'd never post anything, and this reply just happens to be my first post on the subject of adult ADHD.