SAN DIEGO – Methamphetamine abuse may injure the brain, according to new evidence and the experience of clinicians who treat recovering users.
For some, the damage could be permanent. For many, there is an impairment that may be temporary but that interferes with their ability to attend to the short-term treatment most drug abusers get.
“They're just in a fog,” said Dr. Jerome D. Dirkers, medical director of the Montana Chemical Dependency Center, Butte, in an interview at the annual conference of the American Society of Addiction Medicine. “When you try to engage them in treatment, you find they just can't comprehend. If [the user's brain] is not fried, it is at least parboiled.”
In Montana, methamphetamine is the illicit drug most commonly abused by persons coming into treatment, and has been for some time. But Dr. Dirkers has also practiced in South Carolina, where cocaine abuse is more prevalent.
“This [impairment] is something fairly unique to the methamphetamine abuser,” he said.
When the mental fog is temporary, it appears to last about 3–4 months, said Frank J. Vocci Jr., Ph.D., director of the division of pharmacotherapies and medical consequences of drug abuse at the National Institute on Drug Abuse.
“I call it a temporal mismatch, because just when they need their mental faculties–during treatment–they don't have them,” he said in an interview.
A laboratory study of rats given amphetamine three times per week for 5 weeks has shown that amphetamine can induce cognitive deficits. And that study suggested that one of the specific deficits is an inability to make extradimensional set shifts, a cognitive deficit that is also seen in schizophrenia, Dr. Vocci said.
One researcher who has most prominently begun to investigate the effects of methamphetamine abuse on the human brain is Sara L. Simon, Ph.D., a researcher at the integrated substance abuse program (ISAP) of the Neuropsychiatric Institute at the University of California, Los Angeles.
In one of her early studies, Dr. Simon administered a battery of cognitive function tests to recently abstinent abusers and compared them with controls. She reported that there were measurable deficits in the abusers, but that they were specific and perhaps subtle.
In her report, she noted that before her investigation, human studies had looked only at the administration of amphetamine and cognitive functioning, not at its long-term use.
Those studies found, not surprisingly, that amphetamine improved function–probably by increasing focus and concentration–and therefore the notion that amphetamine actually abetted mental function tended to prevail.
Dr. Simon described several of the deficits seen–including problems with word recall and some kinds of abstract reasoning–as being similar to those seen in normal aging (Am. J. Addict. 2000;9:222–31).
Dr. Dirkers noted that methamphetamine abusers in treatment do often seem to function mentally as if they are older than their years.
“They look as though they ought to be functionally well because they are young,” he said. “But they have deficits you would see in someone in their 80s.”
In another of Dr. Simon's studies, PET and structural MRI showed that long-term abusers had severe gray-matter deficits in specific cortical regions, had white-matter hypertrophy that was somewhat greater in the right hemisphere, and had on average 8% less volume in the hippocampus than did controls (J. Neurosci. 2004;24:6028–36).
In a subsequent study using the same technology and complicated functional testing, she reported that abstinent, former abusers have trouble with cognitive vigilance and sustained attention.
Finally, Dr. Simon has compared episodic memory function in abusers who had gone through a drug treatment program and had relapsed, remained abstinent, or continued to use the whole time. Those who relapsed had worse memory than did those who were abstinent, and significantly worse memory than did those who had continued using (J. Subst. Abuse Treat. 2004;27:59–66).
According to a poster presented at the conference, at least some former methamphetamine abusers appear to be aware that their mental faculties are impaired or diminished.
The poster detailed a study reviewing the records of 422 abusers who were followed for 3–5 years after treatment.
Of these abusers, 38% reported having memory, thinking, or concentration problems at some time. Of those who reported such problems, 67% said they were currently experiencing them, said Maureen Hillhouse, Ph.D., who is also a researcher at ISAP.
It is not clear whether this apparent impairment reported by methamphetamine abusers definitely affects treatment outcome. Although some researchers have suggested that methamphetamine abusers have a higher treatment drop-out rate and a higher relapse rate, compared with those who abuse primarily other drugs, other observers have not found evidence of worse outcomes.