5.1 Effects of duration of use

5.1.1 The effects of cannabis differ between na"ve and experienced users. Na"ve users commonly feel either no effect, or alternatively experience intense effects which some find distressing, and which can lead to panic attacks. Many individuals discontinue use at such a point. Experienced users commonly report a sense of relaxation and calm, relief of stress and pain, and enhanced sociability. Tolerance develops both to physical and psychotropic effects, such that the "high" is diminished, but can also be "switched on and off" according to set and setting.

5.1.2 The scientific literature provides conflicting evidence of cognitive and psychomotor impairment. Commonly impairment is most marked in na"ve users under acute intoxication, or with high doses arising from over-use of more potent preparations, whereas many daily users smoke relatively high doses without any noticeable effects on performance, even in studies involving very heavy chronic users.

5.1.3 Although the prevalence of cannabis use falls after age 30, the proportions reporting use to the British Crime Survey in the older age groups showed the greatest proportional increase during the period 1991-96 , with lifetime prevalence doubling in the 40-44 age group (from 15% to 30%, also 8% higher than the 1991 35-39 year old cohort) and trebling (from 3% to 10%) in the 45-59 age group.

5.1.4 The proportions admitting cannabis use within the past year remained relatively stable between the two British Crime Surveys, when successive age cohorts are compared. Thus the relatively low levels of use by the over 30s appear to reflect a generational/cultural effect rather than substantial numbers of users giving up use.

5.1.5 Using the data generated by the IDMU surveys conducted between 1994 and early 1998, we sought to establish whether there is any evidence of increased or decreased levels of cannabis use as a function of the duration of use, and to plot the progression of use over time. Duration of cannabis use was established by subtracting age of first use from current age, and for analyses divided into 6 categories:

1 Missing values & errors

2. Used 0-1 years

3 Used 2-5 years

4 Used 5-10 years

5 Used 10-20 years

6 Used over 20 years

5.1.6 The typical pattern of use appears to be the "up peak down" model identified by Cohen & Sas, whereby users experiment and use a variety of drugs increasingly heavily during the early part of a drug-using career, but after 5-10 years develop a settled pattern of use involving daily cannabis and occasional use of other drugs. There is little evidence for any further escalation after 2 years, indeed average monthly cannabis use declines thereafter with age. There is no evidence of increased levels of cannabis use over the longer term.

5.1.7 Differences manifest themselves in purchase patterns; longer-established users tend buy larger quantities at one time, leaving themselves open to charges of "possession with intent" if arrested, even though a greater proportion of their purchases are intended for personal use. Users of over 20 years standing consume a greater proportion in pipes and eaten, and a lower proportion of tobacco "joints".

5.1.8 It is clear that a substantial proportion of cannabis users continue to use the drug well into middle-age, and that a greater proportion of cannabis users use the drug daily than with other controlled drugs. The pattern of use is broadly similar to that seen with caffeine, which is used several times per day by most UK citizens, and in many cases for similar reasons (relaxation, mental stimulation). Most users consume relatively small amounts - one gram per day or less, although a small number of very heavy users exist. (See Table 2 below).

 

5.2 Cannabis Dependence?

5.2.1 Recent developments in cannabinoid neurobiology have raised the question of cannabis addiction, on the basis of a common action of dopamine release mediated by µ-opioid receptors in the nucleus accumbens. The action of THC and a synthetic cannabinoid were blocked by both cannabinoid antagonist and naloxone, whereas heroin activation of dopamine was blocked by naloxone only. This suggests the action of cannabis/ anandamide to take place "upstream" of the opiate/endorphin system, possibly stimulating the release of endogenous opioids or altering receptor activity, which has implications both for the management of pain and for the treatment of addiction to other drugs. A neurochemical basis for cannabis withdrawal symptoms was also postulated by Fonseca et al, based on CRF release in the amygdala produced by administration of a cannabinoid antagonist to rats pre-treated with a potent cannabinoid agonist (many times more potent than THC).

5.2.3 Withdrawal symptoms from cannabis are reported as including irritability, restlessness, disturbed sleep and anxiety, although the reduction in plasma cannabinoid levels following cessation of use is more gradual than with opiates or stimulants.

 

5.3 Effects on driving

5.3.1 Evidence as to the effects on driving ability is inconclusive. While some studies have shown impairment of psychomotor function and procedures involving complex multitasking (e.g. among airline pilots), moderate doses of cannabis or THC show little or no effect on actual driving performance. Where some impairment in performance is demonstrated, the level of impairment is normally lower than that produced by alcohol intoxication at blood concentrations below present and proposed legal limits. As with other effects, the level of impairment is greatest among na"ve users and/or inexperienced drivers.

5.3.2 The evidence from road accident casualties, and from our own surveys, does not lead to a conclusion that cannabis use is a major cause of road accidents, when compared to prevalence levels within the same age cohort. Our own 1994 survey found reported accident rates per 100,000km, among a survey sample mainly under 30 years old, not to be significantly higher than the national average from all drivers. However we do not yet consider this research to be conclusive, and ongoing studies are being undertaken. 

Table 2 - Effects of duration of cannabis use on patterns of use
Variable	Missing/ errors	Used 0-1 years	Used 2-5 years	Used 5-10 years	Used 10-20 years	Used over 20 years
	Mean	Mean	Mean	Mean	Mean	Mean
Count	n = 119	n = 73	n = 511	n = 1011	n = 812	n = 267
Age***	26.49	19.36	19.51	22.42	28.89	41.47
Age first cannabis use***	15.90	18.53	16.37	15.73	15.64	16.29
Cannabis monthly spending (1)	57.53	29.51	47.61	94.78	68.80	67.18
Cannabis Rating	8.31	8.54	8.58	8.92	8.86	9.04
Cannabis amount per purchase*	9.75	4.96	11.36	15.19	24.29	55.60
Cannabis Purchase unit price*	29.95	17.87	36.79	48.65	67.34	80.77
Average % personal use*	76.74	65.68	68.09	68.51	69.16	77.36
Monthly cannabis use (g)	33.11	12.34	29.99	25.90	24.91	23.25
Monthly cannabis purchase	55.35	36.13	23.92	64.37	53.82	37.33
Monthly cannabis spending (2)	78.22	52.47	54.23	110.9	89.16	97.93
% soapbar resin use***	47.55	47.89	36.48	36.06	42.60	45.61
% "unknown" resin*	28.75	41.39	30.74	21.54	23.92	27.84
% "Thai bush" use*	17.17	31.43	15.45	16.43	10.45	6.94
% "Skunk" use**	28.94	28.27	18.19	24.08	25.72	29.65
% "unknown" bush*	20.86	32.46	29.49	21.46	20.07	17.23
% use tobacco reefers*	64.47	72.44	72.57	73.4	72.45	63.98
% use "neat joints" **	19.33	5.77	4.97	4.45	4.60	7.52
% use water pipe	3.60	8.56	9.53	10.13	8.18	6.64
% use other pipe	4.40	5.87	6.34	5.56	7.47	10.56
Total pipes %	8.00	14.43	15.87	15.69	15.65	17.20
% eat neat***	0.07	0.77	1.17	1.17	1.06	3.80
% eat other food	1.73	3.23	2.19	1.93	2.50	3.66
% drinking	0	0	0.19	0.11	0.08	0.71
Total eat/drink %	1.80	4.00	3.55	3.21	3.64	8.17
% hot knives***	6.40	1.82	1.24	1.32	0.61	0.72
% other smoking	0	0.10	1.20	0.83	1.70	0.73
% other method	0.07	1.05	0.69	0.76	0.29	0.68
Error rate %	0.7%	1%	2%	5%	11%	4%
Reefers per day***	4.81	2.62	4.84	6.25	6.06	5.74
Pipes per day	1.38	0.91	1.98	2.75	2.61	2.85
No. of plants grown	12.82	2.76	19.08	13.08	27.02	30.43
% busted - cannabis***	25.0%	4.92%	14.2%	20.5%	34.5%	49.4%

 82% of respondents answering the "methods" questions correctly added up to 100%,

8 respondents (0.4%) gave totals in excess of 200%.

 

5.4 Health Problems & Benefits attributed to cannabis use

5.4.1 IDMU has conducted surveys since 1994 and developed a database (to June 1998) of 2794 drug users. Questions have included data on drug consumption patterns, attitudes to drugs, driving behaviour and contact with the law or treatment services. All of the users were asked whether they had experienced health problems or benefits as a result of using cannabis, and if so what problems or benefits were reported. The latter were open-ended "write in" questions entered as summaries or quotes. These were subsequently consolidated into a number of different categories, e.g. "amotivation" included quotes such as "tiredness", "laziness", "missed lecture" etc. These categories were not mutually exclusive, as a proportion of respondents reported a number of problems and/or benefits, and a further proportion stated simply "yes" to the general questions but listed no specific problems and/or benefits. As questions about each effect were not specifically asked, the prevalence of such effects within the user population is likely to be underestimated by these results.

5.4.2 Investigation of significant differences between respondents reporting the various problems and benefits and those not reporting such effects included consideration of the following variables (137 variables in total).

(a) Age, Initiation - age at first use of all drugs (tea/coffee, tobacco, alcohol, cannabis, amphet, cocaine, crack, heroin, LSD, mushrooms, ketamine, opium, ecstasy, barbiturates, tranquillisers & solvents), Duration of using all drugs (current age minus initiation age)

(b) Frequency of use of all drugs, and aggregate frequencies for different drug types (coded from 0 - non user to 4 - daily use for each drug)

(c) Monthly spending on all drugs, quantity normally purchased at one time

(d) Ratings of all drugs, plus "soap bar" resin and "skunk", (on a 0-10 scale)

(e) Use of cannabis (monthly use, spending, purchase, reefers/pipes per day, plus types of cannabis used, methods of using cannabis (as % of individual use) & number of plants grown)

(f) Quantitative caffeine, tobacco and alcohol consumption

5.4.3 In the tables below, only differences which were statistically significant, or approaching statistical significance (p<0.1), are listed. No statistically significant relationships were found where these are not specifically stated. Interpretation of results with marginal significance should be undertaken with caution, as on average 7 ostensibly "significant" (@5%) relationships would be expected to arise for each tranche of 137 variables. In questions on initiation ages, monthly spending, purchase and duration of use of specific drugs, plus types of cannabis and methods of cannabis use, missing values are excluded from the analysis, i.e. comparisons are only valid between those reporting some use of/spending on that particular drug/variety/method. Frequency/probability of use data refers to all respondents (missing values coded as "zero" i.e. non-user if space left blank). 

Table 3

Reported Health Problems attributed to Cannabis Use IDMU 1994-98 drug user surveys - combined data, n=2794
Problems	No of reports	%	Comments/ Significant differences from other respondents - p<.01, * - p<.05, ** - p<.01, *** - p<.001
All Problems	588	21.0%	Older initiation to mushrooms , LSD , barbiturates*, tranquillisers* & solvents Higher frequency/ probability of using caffeine***, tobacco***, alcohol***, cannabis***, amphetamine*, cocaine, mushrooms**, heroin*, LSD , ecstasy***, tranquilisers***, all aggregate frequencies***. Lower spending on solvents Higher rating of caffeine*, lower ratings of tobacco**, cannabis*, barbiturates* and soap-bar resin***. Lower use of Lebanese resin and African bush*, neat reefers**, pipes* cigarettes per day , daily tea/coffee , higher use of tobacco reefers
Memory problems	170	6.1%	Higher frequency/probability of using caffeine , tobacco***, cannabis***, amphet*, mushrooms*, heroin*, LSD , ecstasy**, tranquillisers*, aggregate frequency all drugs***, legal drugs**, stimulants***, hallucinogens***, depressants , illegal drugs exc. cannabis**. Longer duration of using heroin Lower ratings of barbiturates* & soap-bar resin* Lower use of African bush , cigarettes per day*
Paranoia	156	5.6%	Older initiation to caffeine , base amphet* barbiturates* Higher frequency/probability of using caffeine*, cocaine*, crack , ecstasy***, aggregate frequency all drugs**, legal drugs*, stimulants***, hallucinogens , depressants*, illegal drugs exc. cannabis*. Longer duration of using barbiturates & tranquillisers Higher rating of caffeine*, lower ratings of tobacco**, alcohol , amphet , mushrooms , LSD & soap-bar resin*. More mushrooms gathered*, lower use of Lebanese resin & pipes*, higher use of home-grown***, higher likelihood of injecting drug use**
Amotivation Included those reporting apathy, laziness and related effects.	133	4.8%	Older initiation to use of caffeine*, tobacco , mushrooms , crack**, solvents* Higher frequency/probability of using caffeine**, tobacco*, alcohol**, cannabis**, ecstasy**, tranquillisers***, aggregate frequency all drugs***, legal drugs***, stimulants*, hallucinogens**, depressants***, illegal drugs exc. cannabis**. Higher spending on barbiturates*** Lower ratings of tobacco*, cannabis , higher rating of tranquillisers . Higher use of tobacco reefers , pipes , fewer cigarettes & cups of tea/coffee* per day.

 

 

Table 3 Continued

Reported Health Problems attributed to Cannabis Use IDMU 1994-98 drug user surveys - combined data, n=2794
Problems	No of reports	%	Comments/ Significant differences from other respondents - p<.01, * - p<.05, ** - p<.01, *** - p<.001
Respiratory problems Included those reporting chest problems, asthma, cough, sore throat or other respiratory tract symptoms.	116	4.2%	Younger initiation to alcohol***, longer duration of using alcohol* and amphetamine . Higher frequency/probability of using cannabis*, cocaine*, mushrooms , tranquillisers , aggregate frequency all drugs*, hallucinogens , depressants , illegal drugs exc. cannabis*. Lower ratings of tobacco** and amphet, higher rating of heroin Lower use of Asian resin and neat reefers , higher probability of injecting drug use
Anxiety/ panic	50	1.8%	Older initiation to tranquillisers* Higher frequency/probability of using caffeine Longer duration of cannabis use*, amphet , mushrooms , LSD and barbiturates* Higher spending on amphetamine , ecstasy , barbiturates*** and tranquillisers** Lower rating of cannabis , soap bar resin**, higher barbiturate rating
Cognitive problems Included those reporting confusion, difficulty in thinking, "head f***ed" etc.	49	1.7%	Younger initiation to alcohol use , longer duration of caffeine use* Higher frequency/probability of using tobacco , cannabis*, legal drugs Higher spending on mushrooms***, barbiturates*** and tranquillisers* Higher rating of caffeine*, fewer reefers per day Older initiation to tea/coffee* and alcohol*, shorter duration of using tobacco , alcohol*, cannabis & amphet*
Overdose/ nausea	35	1.3%	Older initiation to tea/coffee* and alcohol*, shorter duration of using tobacco , alcohol*, cannabis & amphet* Lower rating of cannabis* Higher use of cannabis in food*, fewer reefers*, cigarettes* and cups of tea/coffee per day.
Tobacco- related problems Included respiratory problems and/or nicotine addiction attributed to smoking cannabis/ tobacco mixtures	29	0.9%	Earlier initiation to alcohol* & tranquillisers**, later initiation to ecstasy Higher frequency/probability of using cannabis , and mushrooms* Higher rating of ketamine**, lower ratings of caffeine* & tobacco* Increased use of soap-bar resin , and use in food , lower use of African bush

 

Table 3 Continued

Reported Health Problems attributed to Cannabis Use IDMU 1994-98 drug user surveys - combined data, n=2794
Problems	No of reports	%	Comments/ Significant differences from other respondents - p<.01, * - p<.05, ** - p<.01, *** - p<.001
Dependence Included those reporting dependence, "habit" or problems arising out of difficulties with supply	18	0.6%	Older**, earlier initiation to tobacco**, alcohol Higher frequency/probability of using cannabis , amphet , cocaine , LSD*, ecstasy*, tranquillisers , aggregate frequency all drugs*, stimulants**, hallucinogens**, illegal drugs exc. cannabis** Longer duration of using caffeine*, tobacco***, alcohol , cannabis**, amphet**, cocaine , mushrooms*, LSD**, ecstasy***, tranquillisers* Higher spending on cannabis*, ecstasy*, barbirurates***, tranquilisers*** and solvents . Lower ratings of tobacco & alcohol* Greater purchasing of LSD*** and amphet** More reefers smoked per day
Police/ law problems Included those attributing paranoia/ anxiety symptoms to the legal situation of cannabis	17	0.6%	Higher frequency/probability of using stimulants Lower ratings of tobacco , alcohol* and soap-bar resin* More mushrooms gathered*
Psychosis Included manic depression & schizophrenia	12	0.4%	Older***, later initiation to tobacco*, alcohol , cannabis , mushrooms***, LSD* and tranquillisers** Longer duration of using tobacco**, alcohol**, cannabis**, cocaine*, mushrooms** LSD ecstasy and barbiturates Longer duration of using tobacco**, alcohol**, cannabis**, cocaine*, mushrooms** LSD ecstasy and barbiturates
Other problems	18	0.6%	Older***, later initiation to cannabis**, cocaine*, mushrooms*, ecstasy*** and tranquillisers* Higher frequency/probability of using tobacco*, cocaine*, heroin**, tranquillisers**, aggregate frequency all drugs**, legal drugs , stimulants , depressants**, illegal drugs exc. cannabis* Longer duration of using tobacco**, alcohol**, cannabis* and LSD* Lower rating of soap-bar resin More pipes and cigarettes smoked per day
194 individuals reported two or more health problems

 

Aggregate problems: Significant relationship between aggregate problems and use of stimulants*, and to a lesser extent depressants (including alcohol). None of the other aggregate frequencies approached statistical significance.

Table 4

Reported Health Benefits attributed to Cannabis Use IDMU 1994-98 drug user surveys - combined data, n=2794
Physical Health Benefits	No of reports	%	Comments/ Significant differences from other respondents - p<.01, * - p<.05, ** - p<.01, *** - p<.001
Pain relief	170	6.1%	Older**, later initiation to use of tobacco**, cannabis***, mushrooms** ecstasy* and tranquillisers**, earlier initiation to alcohol use Longer duration of using alcohol***, cocaine*** barbiturates and tranquillisers** Higher frequency/probability of using caffeine*, cannabis***, heroin & tranquillisers* Higher spending on barbiturates , lower on alcohol Lower ratings of tobacco , alcohol** and ecstasy* Greater quantity of mushrooms gathered***, increased proportion of use of "other unknown" bush*, eaten neat* Greater daily caffeine consumption**, lower weekly alcohol units**
Respiratory benefit	67	2.4%	Higher frequency/probability of using cannabis Shorter duration of using caffeine , LSD , solvents* Lower spending on alcohol*, higher on LSD* & ecstasy* Lower ratings of tobacco*, alcohol***, amphet , cocaine* & tranquillisers , higher rating of "skunk"** Greater quantity purchased/gathered of ecstasy* and mushrooms* Greater proportion of use of skunk*, lower proportion of tobacco-reefers*, more reefers smoked per day**, fewer units alcohol per week
Improved Sleep	46	1.6%	Later initiation to tobacco*, cannabis and tranquillisers Higher frequency/probability of using alcohol , cannabis* & depressants Longer duration of caffeine use* Increased proportion of "other/unknown" bush* Fewer reefers per day
Manage Addiction	19	0.7%	Higher frequency/probability of using ecstasy , tranquillisers**, aggregate frequency all drugs , hallucinogens*, depressants , illegal drugs exc. cannabis* Lower alcohol rating* More reefers smoked per day*, more cups tea/coffee per day*
Appetite/nausea	16	0.6%	Later initiation to tobacco , tranquillisers Lower frequency/probability of using alcohol , mushrooms*, LSD*, ecstasy* and aggregate hallucinogens* Lower ratings of alcohol and ecstasy Increase quantity of cannabis purchased , and spending on cannabis**, increased use of pipes*
Epilepsy/ anticonvulsant	8	0.3%	Lower frequency/probability of using alcohol , amphet , LSD*, stimulants , hallucinogens , depressants & illegal drugs exc. cannabis* Longer duration o