I've had this. Please share with your grumpy DH
Painkillers will take edge off but if muscle is genuinely in spasm the only thing that will help is either TIME & REST or an antispasmodic which is what Diazepam (valium) was originally invented for. It's prescribed because very safe actually.
Ibuprofen then Voltarol (which is Diclofenac) will help especially as both anti-inflammatory, but can annoy your stomach
The higher order opiate painkillers such a Tramadol can make you feel a bit crappy all by themselves. Tramadol can make you very useless and unsafe like 'leave the gas on' unsafe.
Heat pad/hot water bottle/ice pack in structured periods with rest can be surprisingly effective.
So here was my own observation: when an area of your back is in spasm, while it is annoying and v.painful but every time it 'catches' it may feel like it is sort of protecting you from further 'proper damage to your spine', so your DH may have strange not quite consciously-formed concern that if he turns off the pain with a pill he may do accidently do himself 'some real damage'. I certainly had that thought during episodes.
A few Diazepam 5mg would definitely help but will make him dozy and also a liability around the house, but would fast forward the recovery.
Medics would only give you a small amount so I wouldn't worry at all about any addiction.
Final unsolicited advice: I went to lots of physio and practitioners and a good Osteo is probably the best place for back issues - they are holistic and sensible- but if YOU wanna fix your back you must do some work with time and effort and a bit of sweat. Any practitioner who just does stuff to your back but doesn't give you any work to do on your own can also become a bit of a crutch, if you have to visit too regularly (chiros being best example, I wld avoid them). Some better osteos will get you do do exercises
A lot of physios will give you Pilates-style exercises but if you have a 'bad back' you probably cannot execute these in the way they are supposed to be done (your core timings may be totally shot, I know someone who did a PhD on this), so they don't actually help. I had to do pre Pilates first, then pilates then yoga. Like 30mins a day of work if you genuinely want to fix yourself. It can be done.
Bad back is miserable existence and it will 'go' again and again if you do not address.
He may be giving himself a hard enough time..frustrating as he is being please do rem give him a (gentle) hug