Does methamphetamine use increase your risk of developing Parkinson's disease?
Methamphetamine (often called 'ice' or 'speed') has been used by one in 70 Australians in the past year, according to data from the National Drug Strategy Household Survey from 2016.
But the stimulant is also used as a treatment for disorders such as ADHD.
Now, researchers are warning there may be a link between methamphetamine use and developing Parkinson's disease, or developing the disease earlier in life.
Dr Julia Lappin
Psychiatrist and senior researcher, National Drug and Alcohol Research Centre, University of New South Wales, Sydney
Dr Norman Swan
Norman Swan: According to the most recent statistics, an astounding one in 70 Australians have used methamphetamine, that's ice, crystal meth and speed (which is powdered meth) in the last year. Ice is a particularly nasty drug causing chaotic destructive behaviour as well as addiction. And if that wasn't enough, a review of the scientific literature has found a moderate risk of developing Parkinson's disease. The lead author was Julia Lappin, a psychiatrist and senior researcher at the National Drug and Alcohol Research Centre at the University of New South Wales, and Julia is in our Sydney studio. Welcome back to the Health Report Julia.
Julia Lappin: Thanks very much Norman.
Norman Swan: So why would you think that methamphetamine causes Parkinson's disease?
Julia Lappin: Well, that's a good question, Norman, and it all comes down to the biological plausibility of the link between methamphetamine, which is metabolised in the body to amphetamine and Parkinson's disease. So Parkinson's disease is a neurodegenerative disorder which is caused by a depletion or loss of dopaminergic neurones in the brain.
Norman Swan: So these are nerve cells that produce a chemical called dopamine which does all sorts of things to our mood and perception and so on.
Julia Lappin: That's exactly right to Norman, So these are cells in the brain…
Norman Swan: And it affects movement as well because Parkinson's causes rigidity, shake, tremor and even a bit of dementia.
Julia Lappin: That's right, and Parkinson's is typically a disorder of the elderly. It's rare before the age of 50, and much more common after age 60 and thereafter. The link with methamphetamine is that methamphetamine is known to cause damage to dopaminergic nerve cells, so these dopamine producing cells in the brain, and that's why we think methamphetamine may give rise to Parkinson's because Parkinson's onsets with the motor features you describe—tremor and rigidity—when there is substantial loss of dopamine cells in a particular part of the brain, the deep nuclei.
Norman Swan: So in other words, they are very effect of methamphetamine on the brain, it's almost like squeezing these nerve cells to death to get the dopamine out of them.
Julia Lappin: That's right, and we know that in the short term methamphetamine users show disorder in their dopamine cells. We also think that over time if you continue to use, that some of that damage to dopamine cells may be irreversible, and that's where the link with Parkinson's comes in.
Norman Swan: So you've surveyed the world literature to see whether there was solid evidence of this. What did you find?
Julia Lappin: That's right Norman. So we looked at two types of evidence. We looked at what's called pre-clinical evidence…
Norman Swan: So is this in animals?
Julia Lappin: Exactly, things that had done in the lab or in animals, and then we also looked at clinical evidence from population studies in general populations and people who use methamphetamine and other stimulants like amphetamine. And what we found was that there is evidence from the cell animal studies that there is damage, as I've said, to the dopamine cells caused by methamphetamine. And in the clinical studies, the population studies, we see that there is an increased risk for Parkinson's disease in methamphetamine's users. Not only are they approximately three times more likely than the general population to develop Parkinson's, but they are also more likely to develop it earlier.
Norman Swan: And is it dose-related; the more use, the higher the risk?
Julia Lappin: Well, that's a great question Norman, because in fact there is many things that we don't know about this association. We don't know what the individual characteristics of the methamphetamine users that predispose people to develop Parkinson's may be…
Norman Swan: So in other words what you're saying is it could be that the person who uses methamphetamine is at risk of Parkinson's or greater risk for some odd genetic reason.
Julia Lappin: Exactly. So we know in the general population that that's true. Some Parkinson's is genetically mediated. For many people there's not a well-known cause. The same is likely to be true in methamphetamine users and it may be, it makes sense, that if someone already has a vulnerability to the development of Parkinson's…
Norman Swan: So you are getting it 30 years earlier.
Julia Lappin: That's right because you are knocking out dopamine cells and you are hastening the onset.
Norman Swan: And does it come on immediately or is there a delay?
Julia Lappin: No. We know that people who use methamphetamine do not develop Parkinson's as a result of immediate use. So in fact it is likely to be a chronic effect. As you continue to use and you lose more and more dopamine cells, you approach quickly that low threshold that you must fall beneath to have the onset of the Parkinson's symptoms. You've lost so many dopamine cells by this time.
Norman Swan: I was on radio this morning talking about this research as a promo to the program and somebody asked me on Twitter to ask you a question. What about Ritalin, what about amphetamines that you use for ADHD? Is this a generic effect of amphetamines and therefore are children who are on Ritalin (and we don't want to scare people to death here) at risk of Parkinson's disease?
Julia Lappin: That's a question that we attempted to interrogate in this study, Norman, and in fact long-term studies of the effects of stimulants used in the treatment of ADHD haven't been done, so we simply don't know what happens to people exposed to the ADHD stimulant medications 20 years, s 30 years, 40 years down the track. And when we think about Parkinson's onset and the fact that it's likely not to onset until the 50s or 60s and the fact that young people being treated for ADHD may be preteen or adolescents, then you've got a 40-year wait until you can try and establish a link.
Norman Swan: Hmm, you haven't settled my mind on this one, or parents listening to us.
Julia Lappin: I think what we can say is that there is no evidence to suggest an association…
Norman Swan: That's because you haven't looked.
Julia Lappin: I have looked but…
Norman Swan: But you can't find.
Julia Lappin: Yes.
Norman Swan: So just take care. And the message for methamphetamines? Just another reason not to use it, basically.
Julia Lappin: It is another reason not to use it. And importantly, we think that many methamphetamine users may have these symptoms but simply not recognise them to be symptoms of Parkinson's or Parkinsonism. So if you have movement disorders, if you notice that for some years you've had a lost sense of smell, difficulty sleeping, there are lots of features now of Parkinson's, both before the true onset of the muscle rigidity and the features that are well known, if you are having these symptoms it may be that you are in the early stages of onset of Parkinson's and it would be well worth seeking help.
Norman Swan: Just so that you can get the treatment early. There is no cure unfortunately. Julia, thanks for joining us. I think thank you for joining us! Always a pleasure.
Julia Lappin: Thanks Norman.
Norman Swan: Julia Lappin is a senior researcher at the National Drug and Alcohol Research Centre at the University of New South Wales.