In today's world, what drug use would be deemed pharmakeia, or sorcery, as it is listed in Galatians 5:20?

Despite the etymological link with pharmakeia, the Church Fathers did not condemn the use of medicinal drugs, but, on the contrary, saw all medical arts as a blessing from God.

I think the most famous writing that relates this is from Basil the Great's Ascetical Works (4th century):

In as much as our body is susceptible to various hurts, some attacking from without and some from within by reason of the food we eat, and since the body suffers affliction from both excess and eficiency, the medical art has been vouchsafed us by God, who directs our whole life, as a model for the cure of the soul, to guide us in the removal of what is superfluous and in the addition of what is lacking. Just as we would have no need of the farmer's labor and toil if we were living amid the delights of paradise, so also we would not require the medical art for relief if we were immune to disease, as was the case, by God's gift, at the time of Creation before the Fall.. After our banishment to this place, however, and after we had heard the words: 'In the sweat of thy face shalt thou eat thy bread,' through prolonged effort and hard labor in tilling the soil we devised the art of agriculture for the alleviation of the miseries which followed the curse, God vouchsafing us the knowledge and understanding of this art. And, when we were commanded to return to the earth whence we had been taken and were united with the pain ridden flesh doomed to destruction because of sin and, for the same reason, also subject to disease, the medical art was given to us to relieve the sick, in some degree at least.

Now, the herbs which are the specifics for each malady do not grow out of the earth spontaneously; it is evidently the will of the Creator that they should be brought forth out of the soil to serve our need. Therefore, the obtaining of that natural virtue which is in the roots and flowers, leaves, fruits, and juices, or in such metals or products of the sea as are found especially suitable for bodily health, is to be viewed in the same way as the procuring of food and drink. Whatever requires an undue amount of thought or trouble or involves a large expenditure of effort and causes our whole life to revolve, as it were, around solicitude for the flesh must be avoided by Christians. Consequently, we must take great care to employ this medical art, if it should be necessary, not as making it wholly accountable for our state of health or illness, but as redounding to the glory of God and as a parallel to the care given the soul. In the event that medicine should fail to help, we should not place all hope for the relief of our distress in this art, but we should rest assured that He will not allow us to be tried above that which we are able to bear. Just as in those days the Lord sometimes made clay, and anointed, and bade wash in Siloe, and on other occasions was content with the mere command: ‘I will, be thou made clean’ whereas He left some to struggle against their afflictions, rendering them more worthy of reward by trial, so it also is with us. He sometimes cures us secretly and without visible means when He judges this mode of treatment beneficial to our souls; and again He wills that we use material remedies for our ills, either to instil in us by the prolonged nature of the cure an abiding remembrance of the favor received, or, as I have said, to provide an example for the proper care of the soul. As in the case of the flesh it is essential to eliminate foreign elements and add whatever is wanting, so also, where the soul is concerned, it behooves us to rid ourselves of that which is alien to it and take unto ourselves that which is in accordance with its nature; for 'God made man right and He created us for good works that we might walk in them.

To place the hope of one's health in the hands of the doctor is the act of an irrational animal. This, nevertheless, is what we observe in the case of certain unhappy persons who do not hesitate to call their doctors their saviors. Yet, to reject entirely the benefits to be derived from this art is the sign of a pettish nature."

When the favor of a cure is granted us, whether by means of wine mixed with oil, as in the case of the man who fell among the robbers, or through figs, as with Ezechias, we are to receive it with thanksgiving. Besides, we shall view the watchful care of God impartially, whether it comes to us from some invisible source or by a physical agency, the latter, indeed, frequently engendering in us a livelier perception of the favor as coming from the hands of God. Very often, also, the diseases which we contracted were for our correction and the painful remedies we were obliged to submit to formed part of the instruction. Right reason dictates, therefore, that we demur neither at cutting nor at burning, nor at the pains caused by bitter and disagreeable medicines, nor at abstinence from food, nor at a strict regimen, nor at being forced to refrain from that which is hurtful. Nevertheless, we should keep as our objective (again I say it), our spiritual benefit, in as much as the care of the soul is being taught in the guise of an analogy. There is no small danger, however, that we will fall into the error of thinking that every kind of suffering requires medical relief. Not all sicknesses for whose treatment we observe medicine to be occasionally beneficial arise from natural causes, whether from faulty diet or from any other physical origin.

So, then, we should neither repudiate this art altogether nor does it behoove us to repose all our confidence in it; but, just as in practicing the art of agriculture we pray God for the fruits, and as we entrust the helm to the pilot in the art of navigation, but implore God that we may end our voyage unharmed by the perils of the sea, so also, when reason allows, we call in the doctor, but we do not leave off hoping in God. It seems to me, moreover, that the medical art is no small aid to continency.

-- Question 55 in "The Long Rules"