Alcohol
Destruction of the protective web

C. W. Leadbeater described how the abuse of alcohol may destroy the protective web that separates the physical from the astral plane:

[There] is a sheath composed of a single layer of physical atoms much compressed and permeated by a special form of vital force. The divine life which normally descends from the astral body to the physical is so attuned as to pass through this with perfect ease, but it is an absolute barrier to all other forces-- all which cannot use the atomic matter of both the planes. This web is the natural protection . . . Any injury to this web is a serious disaster. There are several ways in which injury may come, and it behooves us to use our best endeavours to guard against it. It may come either by accident or by continued malpractice. . . . The malpractices which may more gradually injure this protective web are of two classes-- the use of alcohol or narcotic drugs and the deliberate endeavour to throw open the doors which nature has kept closed, by means of such a process as is described in spiritualistic parlance as sitting for development. Certain drugs and drinks-- notably alcohol and all the narcotics, including tobacco-- contain matter which on breaking up volatilizes, and some of it passes from the physical plane to the astral. (Even tea and coffee contain this matter, but in quantities so infinitesimal that it is usually only after long-continued abuse of them that the effect manifests itself.)
When this takes place in the body of man these constituents rush out through the force-centres in the opposite direction to that for which they are intended, and in doing this repeatedly they seriously injure and finally destroy the delicate web. This deterioration or destruction may be brought about in two different ways, according to the type of the person concerned and to the proportion of the constituents in his etheric and astral bodies. First, the rush of volatilizing matter actually burns away the web, and therefore leaves the door open to all sorts of irregular forces and evil influences.
The second result is that these volatile constituents, in flowing through, somehow harden the atom so that its pulsation is to a large extent checked and crippled, and it is no longer capable of being vitalized by the particular type of force which welds it into a web. The result of this is a kind of ossification of the web, so that instead of having too much coming through from one plane to the other, we have very little of any kind coming through.
We may see the effects of both these types of deterioration in the case of men who yield themselves to drunkenness. Some of those who are affected in the former way fall into delirium tremens, obsession or insanity; but those are after all comparatively rare. Far more common is the second type of deterioration-- the case in which we have a kind of general deadening down of the man' s qualities, resulting in gross materialism, brutality and animalism, in the loss of all finer feelings and of the power to control himself. He no longer feels any sense of responsibility; he may love his wife and children when sober, but when the fit of drunkenness comes upon him he will use the money which should have bought bread for them to satisfy his own bestial cravings, the affection and the responsibility having apparently entirely disappeared.