How much does drinking become sin?

It depends on the individual.

Titus 2:

12 training us to renounce ungodliness and worldly passions, and to live self-controlled, upright, and godly lives in the present age

Click to expand...

1 Peter 5:

8 Be sober-minded [G3525]; be watchful. Your adversary the devil prowls around like a roaring lion, seeking someone to devour.

Click to expand...

Strong's Greek: 3525. νήφω (néphó) — 6 Occurrences

HELPS Word-studies:

3525 nḗphō – properly, to be sober (not drunk), not intoxicated; (figuratively) free from illusion, i.e. from the intoxicating influences of sin (like the impact of selfish passion, greed, etc.).

Click to expand...

1 Thessalonians 5:

6 So then let us not sleep, as others do, but let us keep awake and be sober. 7 For those who sleep, sleep at night, and those who get drunk, are drunk at night. 8a But since we belong to the day, let us be sober.

Click to expand...

When one is no longer sober-minded and has lost control, then he is drunk.

How do we judge that?

The line is not clear-cut. There are some grey areas.

Some Jews wrongfully accused Jesus of being a drunkard, Matthew 11:

19 The Son of Man came eating and drinking, and they say, ‘Here is a glutton and a drunkard, a friend of tax collectors and sinners.’ But wisdom is proved right by her deeds.”

Click to expand...

We should not be too quick to accuse someone of being drunk or intoxicated.

John 2:

10 and said to him, “Everyone serves the good wine first, and when people have drunk freely

Click to expand...

We don't want to be party poopers on special occasions Jesus was there, and he graciously provided even more wine to continue the merrymaking.

Were people at that wedding drunk?

No. That's another picture.

Proverbs 23 paints a more serious situation:

33 Your eyes will see strange things,
and your heart utter perverse things.
34 You will be like one who lies down in the midst of the sea,
like one who lies on the top of a mast.
35“They struck me,” you will say, “but I was not hurt;
they beat me, but I did not feel it.
When shall I awake?
I must have another drink.”

Click to expand...

That is a habitual drunkard losing his mind and his feelings.

1 Corinthians 6:

9 Or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived: neither the sexually immoral, nor idolaters, nor adulterers, nor men who practice homosexuality, 10 nor thieves, nor the greedy, nor drunkards, nor revilers, nor swindlers will inherit the kingdom of God.

Click to expand...

A person who practices being drunk as his lifestyle will not end well.

Similar reasoning can be applied to psychedelic drugs.

Can a high dose of psychedelics open doorways to the demonic?

Yes.