For something often used to describe people and not an analogy like ghoulish or vampiric or cadaverous:

pallid - very pale, in a way that looks unhealthy and not attractive

"Vampiric" is the actual adjective to describe something (or someone) like a vampire.

According to the Collins English Dictionary, as quoted in the Dictionary.com entry for vampiric:

Derived Forms

vampiric ( væmˈpɪrɪk ) or vampirish , adjective

gaunt - extremely thin and bony; haggard and drawn, as from great hunger, weariness, or torture; emaciated.

Dictionary.com

This more emphasises the skinny and haggard nature of their appearance - rather than the pale or sickliness - so you could combine two adjectives, like:

He looked pale and gaunt.

His gaunt and sickly appearance.

If you wish to use an evocative adjective, it could be ghoulish.

Webster's 1913 Dictionary does think that it is synonym to "vampirelike", but it has a broader meaning:

Characteristic of a ghoul; vampirelike; hyenalike.

The meaning of ghoul (originally a flesh-eating ghost of Arab tales) would be:

In popular folklore, an undead or subhuman being, especially one that eats human flesh.

(American Heritage)

Ghoulish is often used in a figurative way, to express the morbid interest of a person for the death of other human beings. But in a proper sense, it would evoke the aspect of a ghoul. Since this word conjures both ideas at the same time, it may or may not be what you are looking for.

The adjectives ashen and ashen-faced (they basically mean the same thing) are used to describe a person who looks unhealthily pale (their skin is slightly grayish in colour) because they are ill or in a state of shock (I guess, a person can naturally look ashen sometimes). The adjective ashen is closely connected with the word ashes. Ashes are the gray powdery substance that is left after you burn something. Here's how the Collins English Dictionary defines this term:

Someone who is ashen looks very pale, especially because they are ill, shocked, or frightened.

Example sentence (one of the two example sentences for ashen in the Cambridge Dictionary):

She was thin and her face was ashen.

Here's a picture of a woman with an ashen face (kind of, looks like a vampire if you ask me):

Such a person is wan:

1a : suggestive of poor health : SICKLY, PALLID

b : lacking vitality : FEEBLE

mw

It goes beyond just pale to describe the haggard, sickly appearance and behavior you want to describe.

Deathly's not bad:

resembling or suggestive of death - his face was deathly pale

People who dress in the aesthetic of the goth subculture would likely be pleased to be deemed they look like a vampire. To your more detailed case to describe drug addicts, my sense is it may fit to some but not all addicts; for the ones that it doesn't really describe there is heroin chic.

I like Etiolated as a metaphorical adjective (describes a person as if they were a plant):

adjective

(of a plant) pale and drawn out due to a lack of light.

Vampirical

It means ‘like a vampire’.

You can say ‘he looked vampirical’.

It means ‘having the traits of a vampire’ or ‘like a vampire’, per the Wiktionary.com entry for the word.

There is always the tried and true "strung-out" or "cadaverous" or "corpselike" i like "he had the look of a worn and deflated pillowcase in need of a wash"