Learn Hardcore Icelandic: Ég er með höfuðverk og mig vantar lyf.

In everyday Icelandic, vera með is the idiomatic way to talk about temporary states and symptoms (headaches, fever, a cold) or things you have on/with you right now. So Ég er með höfuðverk is the natural choice.

hafa (to have) is understood but sounds bookish or less natural for illnesses. You’ll hear Ég hef with abstract things in writing, but for symptoms say Ég er með.
With objects: Ég er með peninga = I have money on me (right now). Ég á peninga = I own/have money (in general).

What does með mean here, and which case does it take?

Here með means “with/possessing” and, in this sense, it patterns like “having.” Með can govern either accusative or dative, with a nuance:

Possession/using/taking along: tends to use the accusative (e.g., with pronouns: Ég er með hann = I have him with me).
In company/together with: dative (e.g., Ég er með honum = I am with him, in his company). For illnesses, think of it as the “having” use. In the phrase með höfuðverk, the form doesn’t show case differences, but the construction behaves like the accusative “have-with.”

Is höfuðverk the normal word for “headache”? What about hausverk or höfuðverkur?

All three are used:

höfuðverk and hausverk are both common in the set phrase Ég er með …. Hausverk is a bit more colloquial.
höfuðverkur is a (masculine) noun; you’ll use it as a subject or with an article: Höfuðverkurinn er slæmur (The headache is bad). After með, people typically say höfuðverk or hausverk.

Why is it mig vantar and not ég vantar?

Because vanta is used impersonally in this meaning (“to lack/be missing”). The person who lacks something is in the accusative:

Pattern: einhvern vantar eitthvað = someone-ACC lacks something-ACC.
Hence: Mig vantar lyf (I need/am lacking medicine). There is no nominative subject, so you cannot say ég vantar.

Is mér vantar lyf ever correct?

In standard Icelandic, no. You’ll hear it from some speakers, but the recommended form is accusative: mig vantar lyf. Stick with mig vantar (or use ég þarf) as a learner.

What’s the difference between mig vantar lyf and ég þarf lyf?

mig vantar lyf = I’m lacking/short of medicine (focus on the absence of something you should have).
ég þarf lyf = I need medicine (focus on necessity). Both are fine in most contexts; þurfa (need) is very common and straightforward.

Can the word order change, like Lyf vantar mig?

Yes. Icelandic allows topicalization:

Mig vantar lyf (neutral).
Lyf vantar mig (emphasizes that it’s medicine you need). Questions: Vantar þig lyf? (Do you need medicine?)

Why is there no article like “a” in höfuðverk?

Icelandic has no indefinite article. Ég er með höfuðverk corresponds to English “I have a headache.” If you want “the,” you use the definite ending: lyfið = the medicine.

Can I omit mig and say Ég er með höfuðverk og vantar lyf?

You will hear that in casual speech because the experiencer is clear from context. However, it’s safer and clearer to keep mig: … og mig vantar lyf, especially in writing or as a learner.

How would I say “I’ve had a headache for two hours”?

Two common options:

Ég hef verið með höfuðverk í tvo tíma.
If you’re male: Ég er búinn að vera með höfuðverk í tvo tíma. If female: Ég er búin að vera með höfuðverk í tvo tíma.

How do I pronounce the sentence?

Approximate, English-friendly tips:

Ég: like “yeh” (final g is soft).
er: “ehr.”
með: “meth,” with the voiced th sound as in “this.”
höfuðverk: “HUH-vuth-verk” (ö is like French œ; ð is the voiced th in “this”).
og: “ohg.”
mig: “mig” with a hard g (often softened in flow).
vantar: “VAHN-tar” (rolled r).
lyf: sounds like “liv” (final f is pronounced like v). Said naturally: a smooth flow with stress on the first syllable of content words.

How do I type ð and ö?

Windows: ð Alt+0240, Ð Alt+0208, ö Alt+0246, Ö Alt+0214 (using the numeric keypad).
Mac: ð Option+d, Ð Shift+Option+d, ö Option+u then o (for Ö, add Shift).
Phones/tablets: long-press d for ð/Ð, long-press o for ö/Ö.

Any polite ways to use this in a pharmacy?

Mig vantar lyf. Gætirðu hjálpað mér? (I need medicine. Could you help me?)
Ég er með höfuðverk. Áttu eitthvað við því? (I have a headache. Do you have something for that?)
If you need a specific item: Mig vantar [nafn lyfs].

Any other idiomatic ways to say “I have a headache” in Icelandic?

Mig er illt í höfðinu. (Literally: I am in pain in the head.)
Mig verkjar í höfðinu. (More formal/literary: my head aches.)
Ég er með hausverk. (Colloquial.)

Does the verb vantar agree with the thing needed? Should it be vanta when the thing is plural?

No agreement here. In the impersonal construction, vantar stays in the default 3rd person singular:

Mig vantar peninga. (I need money.)
Vantar þig eitthvað? (Do you need anything?) Even if the needed thing is plural, you still say vantar in this pattern.

What case is lyf in, and is it singular or plural here?

With vanta, the needed thing is the direct object (accusative). Lyf is a neuter noun whose nominative and accusative forms are the same in both singular and plural. In context, mig vantar lyf usually means “I need (some) medicine” (indefinite, effectively plural/collective).

Do I need a comma before og here?

No. In Icelandic you normally don’t place a comma before og when it links two main clauses: Ég er með höfuðverk og mig vantar lyf.