What stops the body from making serotonin?

Probably the most common thing that stops the body from making serotonin is serotonin itself or chemicals that mimic serotonin or block serotonin receptor sites in the cells of the nervous system.

Serotonin is a neurotransmitter, a chemical that is used by the body to communicate information at the cellular level. This information includes the regulation of aggressive behavior and emotion, body temperature, sleep, appetite, body temperature, cellular division and organ regeneration. Its release also produces a sense of well-being or happiness.

The body regulates serotonin, producing what it needs when it needs it, unless this regulation is imbalanced due to disease or a defect in the organism. The introduction of drugs which mimic serotonin can interrupt the body's natural chemistry. If such drug use is maintained over time, it will cause the body to cease from making its own. This is why the user, if desiring the continued affects or "high" of serotonin must take a larger dosage. The body will respond in kind, further diminishing its own production of the neurotransmitter. If the drug user ever wishes to quit taking the drug, the user must brace for the "crash" since the body will not immediately begin reproducing the drug at sufficient levels, and hence there will be an absence of the drug in the body, causing the body to malfunction either physically, psychologically or both. Hence the craving drug users feel. Over time, unless extensive damage has been done, the body will again begin naturally producing the neurotransmitter.