Patients in the hospital get headaches all the time and I remember during intern year it took a lot of cognitive energy just trying to figure out what medication to give them because no one taught me a general treatment approach. Here's my current algorithm. But seriously just read that article I link towards the bottom of the page, it's a legit beast of an article.

Step 1. Rule out any dangerous causes

If there's anything concerning about the history, or any focal deficit - just get the CT scan right away. Ask your senior/attending but if they aren't available don't be afraid to order it even though you are "just an intern". I was always afraid to order CT scans by myself but honestly, just let somebody know. If they happen to not hear until after it's already been done, it's fine. They won't fault you for being safer rather than sorry (had two patients this last year who would have benefited from earlier CT scans and I wish I had ordered them earlier).

Know how to differentiate primary headache (more benign causes like tension headache, migraine, cluster headache) vs SECONDARY headache (can be from a variety of more sinister causes). A good mnemonic for remembering red flags for secondary headache is 2SNOOP4.

Treat the headache if primary (these treatments specifically are for migraine headache, but can help with tension headaches as well)

1. Turn off the lights, close the door

2. Tylenol or ibuprofen

• Tylenol = 650-1000mg PO every 4-6 hrs, make sure the PRN order lists headache as a reason the nurse can give it. Max daily dose 4g (2g in patients with cirrhosis).
• Ibuprofen = 400-600mg PO every 6-8 hrs, make sure patient is not at risk of GI bleed or has an AKI. I like 400mg because the evidence seems to show it has the same analgesic effect and as you go higher you only increase the risk of side effects.
• Ketorolac (Toradol) = 30mg IV/IM, higher risk of GI bleed, some people teach that patients may get a placebo effect from receiving an IV/IM medication though this doesn't appear to be true per this study. Useful for very nauseous patients who can't tolerate PO.

3. Metoclopramide or prochlorperazine 5-10mg every 8 hours as needed.

• These have the best evidence for treating migraine headache

4. It's mainly supportive stuff at this point with not amazing evidence

• Fluids = consider if they seem volume down or vomiting, usually a good idea as dehydration is a common and known independent risk factor for headaches
• Dexamethasone 10mg = to prevent recurrent headaches, usually don't give unless patient notes it works for them
• PO benadryl 25mg = if you want to try to make them sleepy, limited evidence for preventing extrapyramidal effect

5. Try IV magnesium and repeat dose of anti-dopaminergic

6. Triptans have decent evidence but LOTS of contraindications, and usually are best as an "abortive" medication - eg, given right as the headache starts but not as effective once the headache has already been present for a while. Would only use if the patient is already using it, and definitely not if there is anything concerning cardiac-wise.

* NO OPIOIDS, they don't work for headaches! Source
* The earlier you treat the headache, usually the better the patient will do
* Once you're considering stuff like CGRP antagonists, you should probably be talking to your friendly neurologist. There are two new ones called rimegepant (Nurtec) and ubrogepant (Ubrelvy) which are pretty safe to give and don't interact with other drugs much, but most patients have to bring them in as they are non-formulary.
* Fioricet (butalbital, acetaminophen, caffeine can be a consideration but it has a very high risk of rebound headaches and medication overuse headaches)

Per Nathanael (one of my neurology friends) - his typical migraine/headache cocktail for one time dose:

• Acetaminophen 1000mg PO
• Ketorolac 30mg IV
• Magnesium 2g IV
• Metoclopramide OR prochlorperazine 10mg IV
• Diphenhydramine 25mg PO
• 1L NS bolus

Conan's notes on "migraine cocktails", a common treatment you may see in the ED

Migraine cocktail​

• NSAID (ibuprofen 400-600mg PO, ketorolac 30mg IV/IM if needed but higher risk of GI bleed. Ibuprofen is as effective but there is a possible placebo effect of getting an IV/IM medication, though this is refuted by this study)
• Dopamine antagonist (prochlorperazine, metoclopramide, haloperidol)
• Steroid (doesn't fix headache today but may prevent recurrence, 10mg dexamethasone)
• Antihistamine (PO benadryl, not IV because it gets you high. Supposed to help them get sleepy and prevent extrapyramidal side effects, though evidence for that is poor. Really not that helpful tbh)
• Fluids (not that helpful)

This is a great article overviewing the evidence behind the cocktail: https://www.nuemblog.com/blog/2018/4/26/headache

In summary:

There is good evidence for IV metoclopramide and prochlorperazine (class B recommendation). 
Side effects = orthostatic hypotension, dizziness, akathisia, neuroleptic malignant syndrome
Sumatriptan 6mg subq is also a class B recommendation with NNT of 2.3 for patients to be pain-free at 2 hours

• Difficult to use due to numerous contraindications = don't use in patients with any sort of ischemic disease like CAD, coronary vasospasm, CVAs/TIAs, hemiplegic or basilar migraines, or peripheral vascular disease. Also don't use if another ergotamine or serotonergic agent was used in last 24 hours, or if patient has WPW or arrhythmia.

Tylenol, aspirin, NSAIDs, valproate, IV fluids, and benadryl are class C recommendations
Caution with NSAIDs in patients with history of GI bleed or renal insufficiency
IV fluids were shown in studies to have no benefit in pain management, however theoretically it can help in patients who are nauseous and may be fluid down / orthostatic from anti-dopaminergic agent
Benadryl was not helpful in treatment in migraines or prevent of akathisia, but may be helpful in the TREATMENT of akathisia

Well, just read the whole article I linked. It is really good.