Ég þarf verkjalyf því mér líður illa.

Þarf is the present-tense form of þurfa used with ég. This verb is a little irregular:

• ég þarf = I need
• þú þarft = you need
• hann/hún/það þarf = he/she/it needs

So ég þarf is just the correct standard form, even though it does not have a special ending like English learners might expect.

Because þarf is followed by a noun, verkjalyf, not an infinitive.

Compare:

• Ég þarf verkjalyf. = I need pain medicine / painkillers.
• Ég þarf að hvíla mig. = I need to rest.

Use að after þurfa when the next verb is in the infinitive. Do not use að when what follows is a thing or object.

Verkjalyf is a compound word meaning pain medicine or painkiller(s).

It is made from:

• verkur = pain, ache
• lyf = medicine, drug

So the word literally means something like medicine for pain.

It can be understood as either a general singular-like pain medicine or a plural-like painkillers, depending on context and translation style.

That is because many Icelandic neuter nouns have the same form in the nominative and accusative singular and plural. So verkjalyf can look the same in both numbers.

In this sentence, the important idea is simply pain medication, not a precise count.

Because the sentence is talking about pain medicine in a general, indefinite way, not a specific known item.

• verkjalyf = pain medicine / painkillers
• verkjalyfið = the pain medicine

English often uses no article or chooses between some painkillers, pain medicine, or the painkillers depending on context. Icelandic does something similar with definiteness.

Here því means because.

So:

• Ég þarf verkjalyf því mér líður illa.
• I need pain medicine because I feel unwell.

A learner should know that því can have other uses in Icelandic too, but in this sentence it is a conjunction introducing a reason.

Yes. Af því að is also a very common way to say because.

So these are both natural:

• Ég þarf verkjalyf því mér líður illa.
• Ég þarf verkjalyf af því að mér líður illa.

The shorter því is very common in everyday language. Af því að can sound a bit more explicit or fuller, but both are normal.

Because the verb líða in this meaning takes the person in the dative, not the nominative.

So Icelandic says:

• mér líður vel = I feel well
• mér líður illa = I feel bad / unwell

Here mér is the dative form of ég.

This is one of those patterns you need to learn as a set:

• mér líður
• þér líður
• honum líður
• henni líður

So even though English says I feel, Icelandic uses a structure closer to to me, it feels...

Líður is the present tense of the verb líða.

In this sentence, líða means to feel or to be doing/feeling in oneself, especially in expressions like:

• mér líður vel = I feel well
• mér líður illa = I feel bad

Be aware that líða also has other meanings in Icelandic, such as to pass/elapse:

• Tíminn líður. = Time passes.

So the meaning depends on context.

Because illa is an adverb, and with líða Icelandic normally uses an adverb.

Compare:

• mér líður illa = I feel bad / unwell
• mér líður vel = I feel good / well

Here illa describes how the person feels, so the adverb is used.

By contrast, an adjective would be used differently, for example:

• Ég er veik/veikur. = I am sick.
• Hann er illur. = He is angry / bad / wicked, depending on context.

So mér líður illa is the natural expression for I feel unwell.

Because því introduces a subordinate clause, and the normal order here is:

• conjunction + subject/experiencer + verb + adverb

So:

• því = because
• mér = to me
• líður = feels/is feeling
• illa = badly, unwell

English speakers often notice Icelandic verb-second word order in main clauses, but after a conjunction like því, the clause usually has more straightforward subject-before-verb order.

It can mean both, depending on context.

Possible meanings include:

• physically unwell
• sick or nauseous
• generally feeling bad
• emotionally not okay

In this sentence, because the speaker says Ég þarf verkjalyf, the most likely meaning is physical discomfort or pain.