For 20 years, scientific evidence has shown that long-term use of meth depletes supplies of dopamine by damaging dopamine receptors in the brain.24 Studies indicate that this brain damage can be permanent. Long-term meth users may develop life-long problems with verbal skills, memory, and may even develop Parkinson's disease, an incurable nervous disorder with symptoms of trembling hands and extreme muscle stiffness.6, 11
According to the National Institute on Drug Abuse (NIDA), animal studies show as much as 50 percent of the dopamine-producing cells in the brain can be damaged after long-term exposure to relatively low levels of methamphet-amine. In other animal studies, a single high dose of the drug has been shown to damage nerve endings in the dopamine-containing regions of the brain. The nerve endings do not die, but do not grow back to their original sizes. Researchers also have found that serotonin (another neurotransmitter) and norepinephrine-containing nerve cells may be damaged as extensively.7, 8 9 17, 24, 29
It is often difficult to compare animal studies to humans because very high doses of drugs are used in animal studies. However, scientists using brain-imaging techniques have studied the brains of human meth users. They have discovered that
even three years after long-term meth users had quit using the drug, their dopamine neurons remained damaged.7
Dr. Nora Volkow, director of NIDA, studied brain scans taken of meth users who had been drug free for more than 14 months. The meth users had memory loss and other psychological and physical side effects. The results showed that although most of the damaged dopamine receptors had grown back, the sober meth users still did not show much improvement in their cognitive abilities—their memory, judgment, ability to think clearly, or motor coordination skills—even after a year of being off the drug. Additional brain studies show that the damaged brain cells may never completely grow back to their original size. 17, 29
A 2004 study led by Dr. Paul Thompson, an expert on brain mapping at the University of California, Los Angeles, showed how the brain's center for making new memories, the hippocampus, lost 8 percent of its tissue in meth users. This is comparable to the brain losses seen in early Alzheimer's patients. The study compared 22 people in their 30s who had been using methamphetamine for 10 years, mostly by smoking it with 21 non-drug taking people of the same age. On average, the meth users smoked an average of four grams a week and said they had been high on 19 of the 30 days before the study began. The meth abusers fared significantly worse on memory tests than did healthy people the same age.30 In 2005, the average street price of four grams of meth was about $200 to $250, which means these meth users were smoking about $800 to $1,000 of meth each month.10, 25, 26
Although more studies are needed to clarify what long-term effects are seen at specific dosage levels and with different routes of exposure, these results offer a strong connection between damage to dopamine nerve endings and negative long-term physical and psychological effects experienced by meth users.
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