Alex Dregan and Martin Gulliford

King’s College London 09 March 2012

Illicit drug use and cognitive functioning in mid-adult years

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Background

- Long-term illicit drug use may be associated with impaired short-term and working memory, word fluency, attention span, and cognitive flexibility.

- Other studies found no association between illicit drug use and executive functioning and working memory.

- The relation has not been thoroughly investigated, and the evidence is rather inconclusive, short-term and methodologically flawed.

- Methodological issues: differences in sampling methods, the types of drugs studied, cognitive outcome measures, and length of follow-up.

Alex Dregan

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Study aims

- What is the long-term impact of illicit drug use on cognitive functioning?

- Are diverse drugs differentially related to cognitive imapirment?

- Is there evidence for a dose-response relationship?

Alex Dregan

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Data- National Child Development Study(NCDS) includes all

children born in the UK during the first week of March 1958 (N=17,415)

- Multiple follow-up surveys (birth, ages 7, 11, 16, 23, 33, 42, 46 and most recently age 50) gathering data on a broad range of psycho-social outcomes.

- Illicit drug use –data on 12 drugs collected retrospectively and prospectively from age 16 to age 42.

- Cognitive outcome measures collected at age 50: global cognition, memory functioning, and executive functioning.

Alex Dregan

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Statistical analysis

- All cohort members who took part in the age 42 (N=11,419) survey. - Predictors – current and past illicit drug use (yes/no), class drugs

(high-risk, intermediate, low-risk), length of use and type (ie cannabis, coke, heroin, LSD, amphetamine etc).

- Multiple logistic regression analyses to predict illicit drug usage at age 42.

- Multivariate linear regression to estimate the impact of current and past illicit drugs on cognitive outcomes at age 50 adjusting for age 42 covariates.

- Missing data –separate missing category for each predictor.

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RESULTS

6Alex Dregan

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Illicit drug use at 42 years of age in the study population (N=11,419)

Alex Dregan

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Adjusted ORs (CIs) of predictors for illicit drug use at age 42

Current drug use Ever drug use

Poor health (vs. good) 1.54(1.21,1.96) 1.12(0.95,1.32)

College degree (vs. no qualif.) 1.87(1.43,2.46) 3.31(2.80,3.92)

Smoker (yes/no) 4.33(3.17,5.92) 6.26(5.05, 7.74)

Alcohol problems 1.96(1.64,2.33) 2.03(1.79,2.30)

Depression (yes/no) 1.42(1.17,1.74) 1.30(1.14,1.48)

Single (vs. married) 2.55(2.18,2.98) 1.95(1.77,2.16)

Low social class (vs high) 0.86(0.67,1.11) 0.72(0.66,0.90)

Female (vs male) 0.52(0.44,0.61) 0.52(0.47,0.57)

Alex Dregan

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Adjusted OR for predictors for different illicit drug classes at age 42

High risk Intermediate risk Low risk

Poor health (vs. good) 1.07(0.64,1.77) 1.39(1.07,1.90) 2.27(1.46,3.53)

Long-standing illness 1.02(0.64,1.62) 1.20(0.94,1.53) 1.88(1.23,2.89)

College degree (vs. no

qualif.)

2.22(1.25,3.92) 1.77(1.32,2.36) 1.72(0.93,3.19)

Smoker (yes/no) 2.51(1.35,4.66) 5.20(3.71,7.28) 2.09(1.13, 3.87)

Alcohol problems 2.52(1.79,3.54) 1.92(1.60,2.32) 1.14(0.76,1.70)

Depression (yes/no) 1.74(1.17,2.58) 1.23(0.99,1.53) 3.10(2.07,4.65)

Low social class (vs

high)

1.12(0.63,1.96) 0.84(0.64,1.10) 1.06(0.61,1.85)

Female (vs male) 0.36(0.25,0.52) 0.49(0.41,0.58) 0.71(0.50,1.02)

Alex Dregan

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Descriptive indexes for cognitive measures at 50 years of age in the study population

Sample size Mean(SD)

Global cognition 9,385 26.94(4.78)

Memory index 9,592 11.98(2.94)

Executive functioning index 9,442 11.94(2.90)

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Adjusted B for cognitive functioning outcomes at age 50 as a function of illicit drug use patterns

Cognitive index Memory index Executive

functioning index

Current drug use

Any drug 0.27(-0.10,0.63) 0.14(-0.09,0.37) 0.12(-0.12,0.34)

High risk 0.49(-0.30,1.37) 0.33(-0.16,0.82) 0.16(-0.34,0.65)

Low risk -0.07(-0.92,0.78) -0.06(-0.59,0.48) 0.09(-0.63,0.44)

Ever drug use

Any drug 0.62(0.41,0.83) 0.37(0.24,0.50) 0.23(0.10,0.37)

High risk 0.08(-0.23,0.40) 0.13(-0.06,0.33) -0.08(-0.27,0.12)

Low risk 0.40(0.04,0.76) 0.39(0.16,0.62) 0.02(-0.20,0.25)

Severity of drug use

Never drug dependency 0.25(0.10,0.39) 0.27(0.12,0.42) 0.25(0.10,0.39)

Had a drug dependency -0.27(-1.23,0.69) -0.04(-0.70,0.62) -0.17(-0.78,0.43)

Length of drug use

Both before and at age 42 -0.04(-0.50,0.42) 0.11(-0.17,0.40) -0.19(-0.48,0.10)

Before age 42 only 0.53(0.31,0.74) 0.35(0.22,0.49) 0.16(0.02,0.29)

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Adjusted B for cognitive functioning outcomes at age 50 as a function of type of illicit drug use

Cognitive index Memory index Executive

functioning index

Current drug use

Cannabis 0.28(-0.10,0.41) 0.16(-0.10,0.41) 0.11(-0.14,0.36)

Ecstasy 0.70(-0.61,2.01) 0.40(-0.43,1.22) 0.14(-0.70,0.97)

Cocaine or crack cocaine 0.78(-0.15,1.72) 0.46(-0.14,1.05) 0.34(-0.26,0.93)

Amphetamines 0.50(-0.55,1.71) -0.06(-0.78,0.66) 0.48(-0.24,1.20)

Ever drug use

Cannabis 0.69(0.47,0.92) 0.40(0.26,0.54) 0.28(0.14,0.43)

Ecstasy 0.58(-0.08,1.23) 0.37(-0.04,0.77) 0.15(-0.27,0.56)

Cocaine or crack cocaine 0.43(-0.06,0.91) 0.36(0.05,0.67) 0.01(-0.30,0.32)

Amphetamines 0.49(0.11,0.86) 0.41(-0.17,0.64) 0.07(-0.17,0.30)

Heroin -0.02(-0.94,0.90) 0.34(-0.24,0.92) -0.43(-1.02,0.16)

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Conclusions

- No association between current illicit drug use at age 42 years and cognitive functioning at 10-year follow-up

- Ever drug use association with cognitive functioning implies that any cognitive deficits associated with immediate illicit drug use might dissipate with time

- The association between past use and cognitive function might be explained by residual confounding (ie higher educational level among ever illicit drug users)

- Negative association between drug dependency and long-term illicit drug use and subsequent cognitive functioning

Alex Dregan

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Conclusions ...

- Limitations: self-report, baseline cognitive functioning, reverse causality

- Exploring the influence of illicit drug use over a longer period of time, we were able to avoid the bias caused by false cognitive impairment

- At the population level, it does not appear that past or even current illicit drug use is associated with impaired cognitive functioning in early middle age

- The relation between illicit drug use and cognitive impairment is a complex one: possible that some individuals and groups, such as those with heavier or more prolonged use, could be harmed

Alex Dregan

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Reference

- Dregan A, Gulliford MC. Is illicit drug use harmful to

cognitive functioning in midadult years?A cohort-based investigation. American Journal of Epidemiology 2012;175(3):218-227.

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