Impact of long-term heavy cannabis use Niall Coggans, University of Strathclyde

Niall Coggans, University of Strathclyde

Niall presented a brief background on some aspects of cannabis and health, the finding of a recent study and his conclusions.

Cannabis and depression

Cannabis is a risk factor in the onset of depression

No elevation of risk for depression among early-onset cannabis use (15 years) , but some elevation of risk when used more than twice by age 18

Modest association with heavy or early onset of regular cannabis use.

Little evidence to link depression with infrequent use.

Cannabis and dependence

Dependence occurs in some regular users, but it's not clear what this means

In one study, nearly 1/3 met dependence criteria
Another study found subjective loss of control followed by withdraw symptoms in a subet of users

No correlation between amount or frequency and indicators of dependence

Genetic, early onset of use and tobacco dependence also implicated.

Cannabis and cognitive functioning

Long term use associated with impairment of memory and attention 17 hours after last use Perhaps due to residual comfounding

Cognitive defects found after 7 days, but virtually disappeared by 28 days

Chronic users show mild impairment but little evidence of irreversablity.

Cannabis and respiratory functioning

Chronic inflammatory changes

Higher inflammatory measures, especially where tobacco is also smoked

Correlation between amount of cannabis smoked and decrease in expiratory flow

Confounding and addictive effects of tobacco

The study

Sample and methods

405 participants had used cannabis at least weekly for 10 years
sub-sample of 105 participated in interviews, quantitative and qualitative data in 5 sites in England and Scotland

Snowball sample, stratified by age, gender and socio-economic status

57% male, 43% female
Mean age 33 years

Inclusion of all socio-economic categories, not an exact representation of the general population

Higher percentage educated to further and higher education level or beyond than the general population

Analysis of variance to assess impact of amount and pattern of cannabis use on a range of psychological physical and social functions.

Percent employed participants in each socio-ecomonmic status category

	I	II	III	IV	V
Cannabis sample	5	35	31	10	2
General UK	5	23	48	18	5

Total percentage is less than 100% due to presence of non-classifiable participants.

Cannabis use

Cannabis consumption was defined in terms of amount: (Low, Medium or High) and pattern (Variable or constant)

Composite measure for amount reflected lightest period of use, heaviest period and amount consumed at the time of data collection (alpha = 0.82)

Pattern defined as variable or constant based on self reports of lifetime pattern of use.

Mean amounts during lightest and heaviest periods of use and at data collection (all mean amounts per month in grams)

Cannabis amount groups	Average during lightest period (grm/month)	Average during heaviest period (grm/month)	Average at data collection (grm/month)
Low	1.4	15.7	5.6
Medium	5.7	33.5	15.1
High	25.1	87.1	44.8

Reasons for using cannabis

Enjoyment

Enhanced pleasurable effects in social settings
Relaxant

Preferred to alcohol for some

A small number reported that cannabis alleviated ongoing medical conditions including ME, MS, chronic physicalpain, depression and PMT

Cannabis and other drugs

Use of other illicit drugs, but the main drugs of choice other than cannabis were alcohol and tobacco

The majority of the sample were regular tobacco smokers (90%)
Variation in the level and frequency of alcohol consumption

Higher levels of use of illicit than general population samples, but this was only related to cannabis use in a minor way (<4% variance explained)

Cannabis and Health

Impact on health assessed by GHQ, percieved impact on health and self reports of health problems attributable to cannabis
Cannabis not an important predictor of differences in GHQ scores, despite statistical significant differences (<1.9% variance explained)

Cannabis was not an important predictor of differences in the perceived effects of cannabis on aspects of health(<2.5% variance explained) nor in relation to reported health problems
Clinical examination might have revealed problems due to cannabis eg smoking and lung function.

Effect of amount and pattern of Cannabis use on GHQ scores

GHQ sub-scale	Mean (standard deviation)	N	Effect of amount consumed	Effect of pattern of consumption
A: Somatic symptoms	5.03 (SD 3.66)	402	NS	V+ p = 0.018 eta squared 0.012
B: Anxiety and insomnia	5.0 (SD 4.24)	404	NS	NS
C: social dysfunction	6.70 (SD 2.78)	404	NS	NS
D: Severe depression	2.05 (SD 3.48)	404	H`+` p = 0.039 ETA squared 0.019	V+ p=0,018 ETA squared 0,016

Nb vulnerable users may feel higher somatic problems
High level of use leads to depression, but the link is small

Perceived effects of cannabis on health, sex, memory and life

NB: Statistics were presented, but not explained in much detail to be able to interpret.

Reported health problems

74 (18%) reported respiratory problems - no difference related to amount (chi sq p=0.449) or pattern (chi sq p=0.527)

10 (2.5%) reported pulmonary /heart problems, 5 gave details - no deference related to amount (chisq p=0.205) or pattern (chi sq p=.527)

18 (4%) reported health problems due to their use of cannabis - no difference related to amount (chi sq p=0.996) or pattern (ch sq p=0.579)

Dependence on cannabis and other drugs

55% of this sample met the revised lower criterion of dependence on the severity of dependence scale

62% of the sample met the criterion of dependence in relation to other drug use, which for 79% of the sample meant tobacco or alcohol

Heavier cannabis use was associated with cannabis dependence, although it was not an important predictor of dependence scores
Other factors may play an important role in the development of cannabis dependence.

Other dependent measures assessed

Relationship assessed between cannabis consumption and impulsivity, self esteem, stress, social support, cannabis related beliefs, offending, employment and education

No main effects of cannabis consumption, either by amount of pattern, nor any other interactions could be considered to be important.

Concluding comments

There were only relatively small effects of heavier as opposed to lighter long term cannabis use

The power of the sample size and the inferential statistics used convincingly established that amount or pattern of cannabis use were not major factors

Cannabis was statistically significant in relation to a range of measures, but the amount of difference explained by cannabis use was very small

Cannabis does have some potential for harm

Need for credible public health messages to risks, particularly from smoking as this is the prefered mode of consumption for most cannabis users.

Whilst cannabis does not have the same potential for harm as some other drugs it is not without risks and users need to be aware of these.