Lysergic Acid Diethylamide, commonly known as LSD, is taken by mouth. It has a slightly bitter taste, and is available in tablets, capsules or as a liquid. Acid is commonly sold on a piece of blotter paper, and the user simply chews or swallows it to ingest the drug - without having to buy or conceal any paraphernalia to do so.
LSD has zero physical addiction potential. It is not physically addictive and it is not a drug that you will want to immediately do again. This is not the type of drug where a user experiences withdrawal if another dose isn't ingested within a relatively short period of time.
Psychological Dependence on LSD
However, as with many drugs, users can (and do) become psychologically dependent on LSD. Its pyrotechnic effects and dazzling high can become a distraction, perhaps even an escape from reality for some people. It can become very hard to function in "consensus reality" if you are taking LSD on a regular basis. That, by the way, is an understatement.
People who start to experiment with acid may do so out of curiosity. If they are spending time with individuals who use the drug, they may be tempted to try it to fit in with their peer group. Hearing about the intense colors that go with the hallucinations that Zen users experience may encourage a person to give it a try themselves.
If the first trip is a good one, and the hallucinations are enjoyable instead of being frightening, the user may continue taking the drug to try to recreate this interesting (and seemingly enjoyable) experience. They may not realize that every acid trip is different, and there is no way of knowing in advance what kind of experience they will have.
The flip side to using LSD to try to get a result the user considers positive -- which in this case is to enjoy the experience of an altered reality -- is using the drug to get away from something. Some users start experimenting with it because they are trying to deal with negative aspects of their own lives.
They could be looking for something as simple as a way to avoid feeling bored. Other people who become psychologically dependent on Zen are drawn to it because of a need to step away from the reality of their lives -- to find what they hope is something better -- at least for the hours that they are tripping on the drug.
Tolerance and Acid Use
Tolerance builds up rapidly with LSD. Using the same amount the next day gives a noticeably diminished effect. This wears off after three days to a week. In the meantime, a regular user will need to take a higher dose to get the effect they are looking for. This can be a dangerous thing to do -- given the fact that LSD is a very unpredictable drug.
Cross Tolerance and Zen Users
Cross-tolerance is a phenomenon where a person who has developed a tolerance to one drug also has a certain level of tolerance for drugs in a similar class. There is also some cross-tolerance with other drugs of the same 'tryptamine' chemical family (magic mushrooms, DMT). Even if the individual has never used shrooms or similar drugs before, he would need to ingest a larger dose to start tripping than a person who has never experimented with hallucinogenic drugs.
For a regular LSD user, the cross-tolerance to other psychedelic drugs will last from several days to a week. Stopping the drug use will reduce or eliminate this effect. Cross-tolerance to LSD doesn't apply to drugs like marijuana or uppers, since these substances don't act on the same part of the brain as LSD.