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We all know that meth is a highly addictive, harmful stimulant drug that rots your teeth and makes you paranoid, stupid, unemployed, and homeless -- thereby ruining your life. So just say NO! to meth. Right, kids?
Methamphetamine (meth) and other stimulants are best known for their effects on the dopamine system, and hence for their propensity to be reinforcing and addictive. But meth actually increases the release and blocks the reuptake of all three monoamine neurotransmitters (norepinephrine and serotonin as well as dopamine). Meth addiction can cause alterations in brain function and cognitive performance, according to hundreds of published studies (reviewed in Barr et al., 2006; Baicy & London, 2007). The NIDA website lists a multitude of adverse effects from chronic heavy use:
Long-term methamphetamine abuse has many negative health consequences, including extreme weight loss, severe dental problems (“meth mouth”), anxiety, confusion, insomnia, mood disturbances, and violent behavior. Chronic methamphetamine abusers can also display a number of psychotic features, including paranoia, visual and auditory hallucinations, and delusions...However, a new review article by Hart et al. (2011) concludes that prior studies have exaggerated the harmful effects of methamphetamine on brain structure and function, cognition, mental health, and dental health. In my view, one problem with this endeavor arises in the very first sentence of the abstract:
The prevailing view is that recreational methamphetamine use causes a broad range of severe cognitive deficits, despite the fact that concerns have been raised about interpretations drawn from the published literature. This article addresses an important gap in our knowledge by providing a critical review of findings from recent research investigating the impact of recreational methamphetamine use on human cognition.Many people can use meth recreationally, in modest doses, without becoming dependent. In fact, the review begins by noting the performance enhancing effects of meth in high-functioning, healthy adults who are occasional users. These laboratory studies are conducted in a very controlled environment, using oral administration of pharmaceutical grade methamphetamine. No one disputes that acutely administered meth can have beneficial effects on cognitive performance (Barr et al., 2006):
Numerous studies have confirmed that MA abuse is associated with cognitive impairment. Unlike the acute effects of a single low dose of MA, which can improve cognitive processing speed, attention, concentration and psychomotor performance,77,78 long-term exposure to MA may result in profound neuropsychological deficits (see Nordahl et al2).But how does acute meth affect the performance of meth abusers? Here, the authors cite their own work on the intranasal administration of 3 doses + placebo to 11 meth abusers (Hart et al., 2008). The same computerized battery of 5 cognitive tests was given to the participants during each session. The results in their entirety:
Figure 4 shows how methamphetamine altered performance over time on selected measures.1 As can be seen, methamphetamine improved performance on both of the selected tasks. On the DAT [divided attention task, for vigilance], all active methamphetamine doses decreased the mean hit latency and increased the maximum tracking speed (P<0.05). On the DSST [digit-symbol substitution task, for visuospatial processing], only the two intermediate doses (12 and 25 mg) significantly improved performance. Relative to placebo, both doses increased the total number of trial attempts and correct responses (P<0.03). No other significant performance effects were noted.There is no explanation of why these two tasks were "selected" instead of the other three. Nor is there any indication of how this performance compares to "normative data" or to participants who are not meth abusers. This is a bit ironic, because the most annoying critique within the review is the repeated failure to accept the performance of control subjects as valid. Sure, acute meth did speed up performance on "selected" measures of "selected" tasks, but was this generally better or worse than what's observed in those without a history of long-term meth abuse?
When evaluating whether meth really isn't that bad for you, my focus is on the chronic effects of meth in long-term abusers of the drug. I'll return to this critical issue in the next post.
1 An intriguing aspect of the data is that a massive performance drop was seen from time 0 to time 15 min in the placebo condition. One could speculate that the participants knew by then that they weren't on meth. The "Good Drug Effects" and "Stimulated" self-report ratings peaked at 15 min post-snort, so there's a disappointment-related decrement on placebo.
Figure 4. Selected performance effects as a function of methamphetamine dose and time. Error bars represent one SEM. Overlapping error bars were omitted for clarity.
Baicy K, London ED. (2007). Corticolimbic dysregulation and chronic methamphetamine abuse. Addiction 102 Suppl 1:5-15.
Barr AM, Panenka WJ, MacEwan GW, Thornton AE, Lang DJ, Honer WG, Lecomte T. (2006). The need for speed: an update on methamphetamine addiction. J Psychiatry Neurosci. 31:301-13.
Hart, C., Gunderson, E., Perez, A., Kirkpatrick, M., Thurmond, A., Comer, S., & Foltin, R. (2008). Acute Physiological and Behavioral Effects of Intranasal Methamphetamine in Humans. Neuropsychopharmacology, 33 (8), 1847-1855 DOI: 10.1038/sj.npp.1301578
Hart, C., Marvin, C., Silver, R., & Smith, E. (2011). Is Cognitive Functioning Impaired in Methamphetamine Users? A Critical Review. Neuropsychopharmacology DOI: 10.1038/npp.2011.276
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